PA60 LEVEL 9000 FT UNABLE TO GET FULL PWR ON L ENG; 25 INCHES MANIFOLD PRESSURE VERSUS NORMAL 42 INCHES. EGT LOW ON L ENG. REDUCED MIXTURE; GOT HIGH HEAT WARNING L ENG. REDUCED PWR AND WENT OUT. INCREASED PWR AND HEAT INDICATION RETURNED. SHUT DOWN ENG; NO EMER; CONTINUED TO DEST IPT. FOUND HOLE IN THE EXHAUST MANIFOLD.

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ON 2 PREVIOUS FLTS I HAD HAD INDICATIONS OF DIRT IN A FUEL INJECTOR. ON THE FIRST FLT THE SIT CORRECTED ITSELF PRIOR TO THE NEXT TKOF. ON THE SECOND FLT THE SIT WAS CORRECTED INFLT BY REDUCING THE MIXTURE RICHNESS; THEN RAPIDLY INCREASING IT. ON THIS FLT I NOTICED LOW MANIFOLD PRESSURE ON THE L ENG DURING CLB OUT OF 6000 FT AND BY 9000 FT I ONLY HAD 25 INCHES; WHEREAS IT SHOULD HAVE BEEN ABLE TO PRODUCE 42 INCHES. WHILE IN CRUISE AT 9000 FT I NOTICED THE SAME ENG; THE L ONE'S; EGT GAUGE TO BE LOWER THAN NORMAL. INTENDING TO CORRECT THE LOW EGT INDICATION; I REDUCED THE MIXTURE ON THAT SIDE. THE ENG COMPARTMENT HIGH HEAT WARNING SOUNDED AND I REDUCED PWR AND ENRICHED THE MIXTURE. THE HIGH HEAT WARNING EXTINGUISHED AND I INCREASED PWR. AGAIN THE HIGH HEAT WARNING LIGHT AND SOUND ACTIVATED AND I SHUT DOWN THE L ENG FEATHERING THE PROP. HAVING NO NEED TO DISCONTINUE THE FLT I CONTINUED TO IPT; MY DEST; AND LANDED UNEVENTFULLY. THE PROB WAS LATER DETERMINED TO BE A HOLE IN THE EXHAUST STACK. THE PURPOSE FOR SENDING IN THIS RPT IS TO AVOID ADVERSE CONSEQUENCES SHOULD ANYONE FROM THE FAA SEEK TO VIOLATE ME FOR BYPASSING 2 ARPTS WHICH WERE CLOSER THAN IPT AND COULD HAVE BEEN USED FOR LNDG. AS THE ACFT WAS PERFORMING WELL AT 9000 FT AND I DID NOT NEED TO HAVE ATC RERTE ANY ACFT FOR ME; IT WAS INDICATED THAT THERE WAS NO NEED TO CHANGE MY DEST ARPT; NOR RPT THE SIT AS AN EMER.