my wife's 944 S dodged this bullet. I distinctly remember hearing it as she pulled up; a bit like pulling a chain across a pipe...we had just met so the history of her '44 was a mystery to me. in an instant, I knew precisely what it was and panicked...HONEY! SHUT 'ER OFF...N O W ! ! !
the S only had like 80 some odd thousand miles, a pup; but age and mileage are seldom twins of wear. the chain tensioner ramp pads, those two polyurethane composite slivers that the chain connecting the intake cam with the exhaust ride along aren't service items. they get brittle with age, break apart, and make the chain go slack with disastrous results. there's much documentation and misery to go around to suggest that they ought to be as important an item to change as the timing/balance shaft belt; preferably once for every second time the belts are serviced.
if you happen to be one of the unlucky ones, though, this chap shows you how to go about repairing the head rather than sell an organ on the black market to buy a "used" head which may now be closer to extinction than availability.
best to pay attention to this very important item than go through all this trouble.