I know this is 24 valve section, but my 94 12v has 382,000 miles. In its lifetime, it has had two oil changes.
Yes, two.
One at around 700 miles from the factory fill to Amsoil Marine. One more when the filter system head was updated and the system was contaminated by this procedure.
Fresh filters every 50,000 and samplings done, but that is it.
(The amsoil dealer who bought it new was trying to prove a point. )
He did too!
It sucks a quart every 5,000 or so, but most of that ends up on the ground, not out the pipe. VERY little, if any, "breather exhaust" on it also.
I agree that you need to check things out. Could save a bundle to find it now instead of later.