When do u change the 8 plate oil coolers that mount near the flywheel. They don't look great but don't leak either. After a couple years change them or wait for them to leak

If they are working fine then leave them. I have seen them many, many years old, looking like hell and still working fine. As a matter of fact, I can count on one hand the number of plate coolers that I have seen go bad.
Eddie

if your worried about it unscrew the anode
2the bottom of the cover and see what it looks like.i bought a boat last year that had that set up.one side was so caked w/salt that it had almost ate through the cover,no anode left.the other side was replaced some time ago and looked almost new.i guess the old owner never flushed the engine after running in salt water.i agree w/eddie though,if its not broke,dont fix it.