I have worked on 951's for years with no real issues, they don't like water ingestion and will kill a top end in short order if you submerge it , they don't like any kind of aftermarket starters or starter clutches , but then what engine does really , other than that no real issues to speak of , regardless of the horror stories you hear I have never seen one throw a rod or bust a case , I am sure it happens to someone some where but the crankshaft is pretty beefy on a 951.
OEM wear rings suck, I usually use the solid type wear rings , if it has gray fuel lines on it ditch them , replace the lines and clean the carbs , make sure all the flaps are on the air intakes and the rubber boot is around the exhaust joint to keep water out of the engine .