A C414 engine was shutdown; an emergency declared and the flight diverted to an enroute airport after an oil loss resulted in decreasing oil pressure. Pliers in the oil cooler punctured it and caused a leak.

Narrative

Engine shutdown in flight due to oil leak and loss of oil pressure. Flight began with two scheduled legs; first stop ZZZ and second ZZZ1. When turning base leg at ZZZ pilot in command noticed oil on number 1 engine cowl. After landing on the turnaround inspection pilot checked oil and found oil to be full at 12 quarts. Pilot took rag and wiped off engine cowling. Ordered aircraft serviced with fuel and took off on second leg of flight. Oil leakage continued to get worse and worse as the flight progressed. The pilot radioed to change destination to ZZZ2 to get maintenance to look at the engine. While heading to ZZZ2 oil pressure began to drop off. The pilot elected to do a precautionary engine shutdown on the number 1 engine while it still had oil in it. The pilot elected to divert to ZZZ3 due to close proximity; excellent facilities; and maintenance availability. The aircraft was landed at ZZZ3 by visual approach backed up by the ILS on one engine. After inspection by FBO Maintenance found 10 inch needle nose pliers logged in number 1 engine oil cooler. The nose of the pliers had poked a hole in the oil cooler causing the oil to leak from the oil cooler.