After considerable effort, this problem is resolved.
In the end, I did replace the clutch and cover plate - largely because I had the gearbox out and had the opportunity.
I also installed the Moss rear main seal kit while I was there, which was not as challenging as I had anticipated. Instructions were quite good, as were the drill guides supplied in the kit. All tolled, it took about 2 hours.
I also replaced the master and slave clutch cylinders. The slave was original and obviously in need of replacement as the piston moved too easily in and out of the cylinder. When a newslave was installed, the throw on the clevis pin and thrust bearing was markedly increased. I had rebuilt the master last year and assumed it was ok, but when I replaced it with new, the throw on the clevis pin and thrust bearing increased siginifcantly again. Also of note: there were no fluid leaks evident for either, which might suggest a rebuild or replacement was in order.
If I had to do this again, I would start with replacing the master and slave cylinders, as it is far cheaper and easier than going directly to the clutch. That said, with the gearbox out, I was able to fix a couple of small leaks, clean it and the OD out properly and do the main seal.
Thanks for the help on this everyone,
Steve