So I've removed and replaced these PC's three times now and still leaking- looking for where the problem could be. Cleaned everything thoroughly. Tried different torques within the specified range. Even tried installing the thin sealing rings, even though the length of PC tip projection is within spec. Any suggestions? Thread sealant on the collar nut maybe? Definitely leaking between the collar nut and female threads in the aluminum head.

The background information here: Installing a #22 head where it was previously a #14 head, and I'm using the old pre chambers from the 14 head. they appear to be in serviceable condition. Maybe something I'm overlooking here.

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1987 300SDL