BE36 COM PLT EXPERIENCES AN EXHAUST LEAK TRANSITIONING ABOVE DFW CLASS B AIRSPACE.

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I WAS IN CRUISE PHASE OF A FLT FROM PWA TO RKP; VFR AT 11500 FT. MY ACFT IS A TURBO NORMALIZED BEECH A-36/G. I WAS COMMUNICATING WITH FORT WORTH REGIONAL APCH WHILE FLYING ABOVE THE CLASS B AIRSPACE. I WAS NEAR THE SOUTHERN EDGE OF THE LATERAL EXTENT OF THE CLASS B AIRSPACE; SW OF FORTH WORTH WHEN MY WIFE SMELLED A BURNING ODOR. UPON INSPECTION OF GAUGES; I NOTICED A DROP IN MANIFOLD PRESSURE OF APPROX 6 INCHES. REALIZING THE POTENTIAL OF AN EXHAUST FAILURE AND POTENTIAL FIRE; I IMMEDIATELY CONTACTED APCH AND ADVISED THEM OF MY DILEMMA AND EXPRESSED AN IMMEDIATE NEED TO DSND. I ADVISED THAT CLEBURNE; TX; WAS AHEAD AND DECIDED I WOULD TRY THAT. I WAS ADVISED THAT I HAD TFC AT 12 O'CLOCK POS AND APPROX 5 MI AT 11000 FT. I ADVISED TFC IN SIGHT AND WAS TOLD TO MAINTAIN VISUAL SEPARATION AND DSND FOR CLEBURNE; TX. I WAS ASKED THE NATURE OF MY EMER AND I ADVISED THAT I WAS NOT DECLARING AN EMER BUT THAT A DSCNT WAS NECESSARY FOR SAFETY. I WAS OFFERED OTHER POSSIBLE ARPTS AND GIVEN COURTEOUS AND PROFESSIONAL ASSISTANCE BY THE APCH CTLR UNTIL WE WERE HANDED OFF TO CTR. THERE WAS NO MENTION OF ANY PROB (VIOLATION OR DEV) AND I HAVE NO REASON TO SUSPECT THAT THERE IS ONE. I WAS SIMPLY VERY BUSY AT THE TIME CANNOT SAY FOR CERTAIN WHETHER I ENTERED CLASS B OR WHETHER I WAS SPECIFICALLY CLRED TO DO SO. I WAS CERTAINLY CLRED TO DSND. UPON REDUCTION OF MANIFOLD PRESSURE FOR DSCNT; THE ODOR CEASED AND ALL GAUGES LOOKED NORMAL. WE WERE AT 9000 FT AND OVER CLEBURN AT THIS POINT SO WE NOTIFIED CTR THAT WE WOULD CONTINUE OUR DSCNT AND GO INTO WACO UNDER A NORMAL DSCNT PROFILE. CTR HAD BEEN ADVISED OF OUR PROB AND WE WERE AGAIN TREATED WITH A PROFESSIONAL; CARING ATTITUDE. UPON BEING HANDED OFF TO WACO APCH; WE WERE ADVISED THAT AN OVCST LAYER AT APPROX 3000 FT AGL HAD DEVELOPED AND WE WERE GIVEN AN IFR CLRNC TO DSND THROUGH THE UNDERCAST. WE WERE AGAIN TREATED WITH PROFESSIONAL RESPECT BY OUR CTLR; OFFERING US A FIRE TRUCK OR ANY OTHER HELP HE COULD OFFER. WE DECLINED; SEEING NO IMMEDIATE NEED AND AS WE WERE IN VFR CONDITIONS; PROCEEDED TO ACT FOR A NORMAL VFR LNDG. WE EXITED THE ACFT AND INSPECTED THE ENG IMMEDIATELY. WE FOUND THAT THE EXHAUST LEADING INTO THE TURBO HAD CRACKED AND SEPARATED CAUSING THE REDUCTION IN MANIFOLD PRESSURE AND A SUBSTANTIAL EXHAUST LEAK. THE LNDG WAS NECESSARY IN THE INTEREST OF SAFETY AND PRESSING ON COULD HAVE BEEN COSTLY INDEED. I HAVE WRITTEN THIS RPT FOR SEVERAL REASONS; THE MOST OBVIOUS BEING A GENERALIZED COVER MY REAR END APPROACH. I DO NOT HAVE ANY REASON TO SUSPECT THAT THERE WAS ANY VIOLATION OR IMPERMISSIBLE DEV; BUT THINGS WERE HAPPENING FAST AND I WAS A BIT DISTR BY THE THOUGHT OF FIRE. SECOND; I WANTED TO STATE THAT AGAIN; AND MANY TIMES PREVIOUS; CTLRS HAVE BEEN HELPFUL NOT ONLY AS TOOLS BY WHICH TO NAV AIRSPACE BUT; AS PEOPLE; CONCERNED AND HELPFUL. THE CALMING EFFECT OF A GOOD CTLR; AND THEY ALL WERE; CANNOT BE OVEREMPHASIZED. I CONTINUE TO FLY EVERYWHERE UNDER ADVISORIES FOR THIS REASON.