My 2003 X5 3.0 (170K) has repeatedly misfired and shown a p0301 code indicating a cylinder 1 misfire, I replaced the coil and the problem goes away only to reappear withing a month or two. Always cylinder #1. I've replaced the coil twice plus the original coil.

Any ideas?
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2003 X5 3.0 - 200K
2019 Subaru Forester - 80K
1986 Merkur XR4TI Intercooled - 160K