Porsche's are pretty reliable, its when they get into disrepair by stupid owners is when you're fucked. Granted parts are expensive and an engine rebuild would be probably 1arm and 1leg with some change back, but if you get it done right you'll have no problems for a long time. My buddies dad owned at mid 70s 911, the timing chain blew and he had to rebuild the engine. He knows the parts manager at Motorwerks so he got a deal on making the motor in RS spec. Even in 1981 it cost $3600 to fix everything.