My 94' E500 has 108,000 miles, with ticking that increases in frequency with engine revs. Ticking is only when engine is full operating temperature. No ticking at all when cold.

Using a stethoscope, I find the sound is most pronounced just behind oil filler cover forward end of right cylinder bank. I've had all oil tubes (rubber) on right side replaced, and this produced no change. Did not change left side, since ticking is on the right.

Oil pressure at idle is consistent 2 bar, without drop or fluctuation, and max otherwise. I've just about 100 miles ago switched from Mobile 1 Zero-40 (used by prior owner and dealer) to Castrol GTX 20-50 (mineral).

Some mechanics have indicated tensioner on timing chain could be going, however, the noise does not appear to be in that area. One mechanic theorized that tensioner has a hydraulic ram that could work better when engine is cold and oil is more thick, but again noise is not in that area. This particular independent throws his hands up, then and suggests replacing all tappets, though he reported they appeared OK when he pressed on them during oil tube replacement. One mechanic recommended using Prolong, however, that sounds like it will create more problems than it will solve.

Any suggestions appreciated.