Timing chain guides. In retrospect, you should have replaced those with the head gaskets, "while you were in there".

It sounds like your mechanic will do a proper diag...

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2002 X5 4.6is - Titanium Silver / Black Alcantara - Dinan Stage 2 - Bilstein/Eibach - Brembo BBK ----SOLD---
1993 318i - Brilliantrot / Tan - bone stock daily driver