I agree with all of the experts above as long as the lower end, compression
is OK. I suggest that once the head is off:
Do a valve job.
Check all push rods to make sure they are straight.
Set the valve spring loading.
Replace the head bolts.
Get a spare gasket kit.
These are all simple things for a diesel
mechanic and are small incrementals once the head is off.
This is not the end, just fix it. We have Westerbeke
6 115 Hp main and Westerbeke 12.5 Kw (75Hp) 4 cyl generator
. Both 1984. They run very well.