The valves have been checked quite recently. Within the past 4 months. The car has been in the shop 4 separate times for this same issue. My indy is good but hasn't been able to resolve it.

The top end has been rebuilt at around 160k Miles. As of then compression is good. I don't know if he has checked it again since then. The mechanic is quite thorough though.

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Current
2006 E320 CDI, 57K bought at 67K "Liesl"
1986 190E 2.3-16, 198K bought at 56K "Brigitta"
1987 300TD (Chuggin Along), 292K "Friedrich"
1995 E320 Wagon, 200K "Louisa"

Past
1987 300SDL, (sold) 125K, bought for 1$ "Kurt"