Mechanical oil pressure gauge is #1 thing to do. STOP "throwing" parts at it(your words). I agree with Aurelias, you have 2 problems. Your misfires are from your timing chains being toast. Trust me, I know it is an "N" 62, not "M". I have an N62 in my shop that came out of an 05 that the guides failed and engine was toast. SO, it does happen. But, you keep throwing parts at it and hope it is an Oring. That engine is done.

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Dave S.
Northeast
2003 4.6is
2005 E53 4.4
2003 E39 Msport(a REAL ONE!)
1959 Fiat 600