This is a 1983 R65 with 12,000 miles. It sat for years before I purchased it. All the external rubber was shot. I imagine many of the internal seals are bad as well.
I will probably replace:
Rear main seal.
Oil pump O-ring.
Gearbox input seal.
- as recommended by Ted Porter.
But I wonder if anyone has a best guess of the source of the leak. My guess is that it's the transmission seal from what I can see in the photos, but due diligence is going to make extra work for me and make me replace the lot.