E46 BMW M3 Cylinder Head Oil Leak

I've been chasing an oil leak on a BMW M3 for about a year now.  Pictures are worth a whole lot more than words, so here are some photos of the symptom:

Oil pooling inside the transmission bell housing:

Thought it was coming from the rear main seal, so replaced that first:

During this job, I noticed that the leak looked like it originated higher up, from somewhere behind the cylinder head:

So, I decided to swap out one of the camshaft position sensors thinking the o-ring around it might have been the source:

Finally had it traced down to screw in the back of the cylinder head.

Here's the BMW diagram of the the part itself (Part #14 in the diagram below)

I'll do a full write-up once the repair is concluded.