Follow-up: OK, I found...uhhh...the problem:
On the RH side, the rearmost fitting was a bit loose but I'm pretty sure it was still performing OK. The cam, bearings, and followers look good. The cam and followers were replaced 15K miles ago.
But....
1. The LH oiler fittings were melted except for the one at the front.
2. The oiler tube was partially plugged at the fittings by melted plastic.
3. The cam is blackened and the rearmost lobe is eaten; the rest don't look too good.
4. Many followers are worn.
5. The cam bearings are blackened.
Other than that, no problemo
Well, it's obvious what needs to be replaced, but I am worried about what went wrong first, and if I replace these parts, will it happen again?
Basically, what the heck happened? I am absolutely, positively sure beyond any doubt that the fittings were installed properly and entirely in their seats, touching. If they weren't, I think I would have known a year ago. I had replaced the fittings of both sides when I did the major work 15K miles ago. The only thing that I can think of is that this engine was obviously not maintained very well (considering how I bought it) and maybe I should have replaced the LH valvetrain stuff when I replaced the RH parts.
I'm going to TRY to boneyard this stuff, but if I can't get a good price, I'm going to have to think about other options. This is very, very depressing.