The fact that the noise and behavior is intermittent means to me that the engine is sound and is worth fixing. The repair(s) can be relatively low cost if you turn your own wrenches.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC