If anyone is interested, here's the fix:
I purchased part # 6821262-01. As far as I know pretty much any mirror from any late model BMW can work, the biggest concern is the mount. Make sure it's compatible to save yourself having to figure out a new one.
My original plug had two wires: one 12v powering the red alarm light, and one grounding it. The new mirror had four pins. The two missing are the 12v and ground for the autodim, homelink buttons and compass.
I purchased two of part # 61.13.0.005.197. These are pinned wires to be added to the connector and tapped into an existing 12v and ground.
I opted to splice into the rain sensor, for two reasons. It runs parallel to the mirror plug, and is 'semi-switched', in that it powers down once the car goes to sleep, about 15 min.
The rain sensor plug has three wires. You're concerned with the farthest left and right. The red wire is your 12v, the brown wire is your ground.
The 12v wire gets pinned in to #3 on your mirror plug, the ground gets pinned in to #10.
And that's it. Pretty simple. I paid $50 for the mirror on eBay and $8 for the wires from the dealer. Good to go.
