Pilot reported excessive oil consumption and oil present on the Rotax 912iS lower engine cowl. Pilot reported increasing oil temperature during arrival and continued to landing at destination airport where the engine seized during taxi off runway. The reporter recommended the aircraft manufacturer correct the oil tank venting discrepancy as the oil tank vent outlet does not have a bypass.

Narrative

Cross country flight departed from ZZZ1 enroute to ZZZ. Total flight duration was 4.3 hours. As I landed at ZZZ and taxied off the runway my Rotax 912is engine seized up. Can't even turn the prop by hand. I had flown about 14 hours. The engine performed flawlessly. Spent much of the trip up high above the clouds. It was magnificent. The last flight was about 4 hours long and after a 20-30 minute hold; I flew the arrival. 1800 [ft.] MSL at 90 knots. Seemed like it took more throttle than usual to maintain 87-92 knots. I was running it at the top of the green arc on the tachometer. Noticed after a while the oil temperature was getting in the yellow. I pulled the throttle back until the Eco indication illuminated. Oil temp went down but not back to green. Then the Lane A warning light began to flash. I cycled it but it always went back to flashing. 'Two Strikes'; now I was getting a bit worried. I was at about 1000 [ft.] AGL in this tight pattern of hundreds of aircraft. With throttle pulled back a bit I continued the approach at about 80 knots and landed on Runway XXL. Uneventful landing other than the flashing light. I was held for a few minutes waiting for other aircraft to cross the taxiway intersection. I opened the door to get some cooler air. I heard an unusual noise from the engine as it idled. When the ground person waved for me to pull up; I slightly advanced the throttle and the engine locked up. Done! About 30 hours since oil change. About 134 hours on engine. I check the oil each morning before flying. This engine never needed oil added between oil changes. But yesterday I noticed oil on the fuselage from the breather tube. I wiped it off with an alcohol wipe. When I checked the oil this morning; it was at 25% of the safe zone. It had always been at 50%. So I thought it just blew some out on the long cross country. I did not add any oil.Volunteers helped tow and push my plane to the amphibian seaplane parking area. Once I tied it down; I went looking for Rotax. The following is a postmortem of the engine when it was removed and disassembled by the Rotax distributor:Traveled to ZZZ after to remove 912iS Sport from Super Petrel after engine stopped during taxiing. Removed engine from aircraft at hangar and transported to Company 1 for inspection. Note that downloading data and fault logs was attempted (one week before engine removal) but ECU (Engine Control Unit) would not come online. Both Lane A and Lane B switches were turned on; but indicator lights would not turn on and BUDS 4.0.0 would not connect.Engine was completely locked up as propeller would not turn frontward or backward. No external damage found. Upon initial aircraft inspection noticed oil running down side of aircraft from the fuselage oil tank vent port located on the pilot's side under lower wing; perpendicular to air flow. No bypass found in oil tank vent line per Rotax 912iS Sport Installation Manual section 79-00-00 pg. 10. Engine coolant was full and clean.Total oil quantity recovered from engine was 2.43 liters (2.57 quarts): This includes oil tank; oil lines; 2 oil coolers; crankcase; and oil filter. The oil tank; oil lines; 2 oil coolers; and oil filter held 1.74 liters (1.84 quarts); and the crankcase held 0.7 liters (.74 quarts). Metal debris was found inside all oil system components including oil tank; oil lines; 2 oil coolers; crankcase; oil pump; and oil filter. Note that oil lines were connected correctly per Rotax 912iS Installation Manual section 79-00-00.Valve train completely intact and in good condition: Lifters show no signs of surface degradation. Camshaft journals and camshaft bearing surfaces in crankcase show normal. All rocker arms and valve spring assemblies in place as normal. Very little or no wear on valve spring shims 926210. #3 cylinder intake shim shows more wear than the rest; but nothing that can be felt with the edge of a fingernail.Cylinder #4 large end connecting rod bearing failed: After removing cylinder heads and cylinders; found #4 cylinder connecting rod failed at the large end. Camshaft surfaces and pistons show impact damage from flying debris during rod failure. Checked oil galleys in crankcase and crankshaft for blocked ports. All oil passages show clean and open. Crankshaft plain bearings and crankshaft journals show normal except for a few areas where contaminated oil was being fed through the oil system. Cylinder #4 piston shows that it contacted cylinder head after large end rod failure.Data logs show no oil over temp or oil pressure below minimum: The data and fault logs were downloaded from the engine ECU located behind pilot's head at time of engine removal. No faults were present for exceedance of max allowable oil temperature or loss of oil pressure below minimum spec. Data logs forwarded to Name for additional investigation and comment. It is noted that upon turning on Lane A & Lane B with engine off; Lane A light flashes as the ECU is notifying pilot that it indicates Lane B light was not functioning. Removed Lane B bulb from aircraft and tested normal (12V incandescent). Further investigation will be required to remedy this fault as well as discover why log extraction was attempted one week prior and ECU would not turn on nor BUDS 4.0.0 connect. Also noted that at time of engine removal BUDS showed cylinder 3&4 EGT at 1000degF =/- even though engine had been inactive for one week.Summary: It is of my opinion that the engine did not starve of oil; causing #4 large end connecting rod failure. At no time were low oil pressure warnings recorded by the engine ECU; and the lubrication system still contained 2.43 liters of oil. There is no evidence of valve train bounce (aeration) evident. Although the oil tank vent line routing is not compliant per the Rotax 912iS Installation Manual; and oil was present on the fuselage; I don't believe it the cause of this failure. That being said; I still strongly recommend that the aircraft manufacturer correct the oil tank venting discrepancy as the oil tank vent outlet does not have a bypass. The engine; oil coolers (2); and oil lines will have to replaced. Please advise as to any additional data; RMAs; or pictures required.