Thanks for all the good ideas. I've ordered a new breather and Nikasil kits/gaskets from MG Cycle. I'd planned on doing a full tear down this winter, replacing all engine seals, putting in the Nikasil's, and new clutch, etc, new wiring harness, etc - the Nikasil's are evidently getting scarce, so I though I'd grab them with Rick & Gordon still had a set.
I reevaluated the plugs and decided the right side is just a bit rich, not oily (hasty "wanted it to be" diagnosis before). I'll go ahead and replace the breather (it was original - can't hurt). If it keeps blowing oil I'll see if it goes all the way down to dangerous levels. If so I'll probably go ahead and do the Nikasil's now. If not, I'll ride it til Winter when I plan to do the full tear down anyway.