First, happy new year, folks, it's been a while since last seeking wisdom from the forum. Swapping out pitted tubes on my nc-35, what an experience separating the block from the tube, but my problem is the o-ring between them, which is not on the parts breakdown. I do not want to re use a 20 year old o-ring. Can ya help a guy out with what the proper ring is?

I think the short answer is that Showa don`t intend you (or even your bike dealership mechanic) to separate the bottom casting from the stanchion - that`s why only the complete assembly is listed as a spare part and (as you have discovered) it is assembled with mega strength thread lock. The casting is also pinned in place on some later Honda models.

The practical answer to your issue is measure the original O-ring and source a replacement from your local bearing/seal supplier.