How many miles on your truck?

Did you find any metal shavings in the motor? Or are you (they) just speculating due to the worn case?

Since the guides are so cheap (parts), and it sounds like you already have the motor open, would it not make sense to flush the motor and throw new chain guides on it?

4.6 motors are so hard to find, it was one of the factors that made me leery about the 4.6. You could think about swapping in a 4.4... in my speculation it should bolt right up and run on the existing ECU.

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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