Got to do some work on the valve stem seals.
I ordered a Powerbuilt valve spring compressor (presently going for $20 + free shipping on eBay)
and a Lisle valve holder. The valve spring compressor is very similar in design to the units offered by Moroso, Summit, Jeg's and Probuilt but at a much cheaper price.
I popped off the passenger-side valve cover and found the source of the leak: a small piece of an older valve cover gasket. Can't believe I missed that. No more working at night. Lesson learned.
I hooked up the valve holder to the compressor. There were no directions included so I set it to 100 psi. I had a few moments of frustration because the valve spring compressor shaft that bolts onto the rocker stud was too big. The packaging said it was for both 3/8" and 7/16" studs. Turned out the the shaft has different threads on each end and has to switched. That required popping off a c-clip and reassembling it.
Once the compressor was correctly set up, I removed the retainer, spring and seal from the #2 cylinder exhaust (?) valve (the very first one on the right).
Now, I need help identifying what I've got. Based on what I've seen and read so far, I believe these are the positive stop seals.