home from work to home and as I pulled in driveway an Isuzu Trooper runs across my front yard and Tee-boned me!
Holy hanna, I hope you got something more than a I am sorry.
When I was looking for parts, our web site is great! other common sources is everything from Amazon, ebay, I have gone into my local Menards, and Fastenal for rubber odds and ends. any web site that is selling things with cheaper shipping, IE if your getting more than $100. worth of stuff, most are good, with the free shipping, but if you just need a small envelope full of O-rings, then its ten bucks for s/h. ebay tends to still have gasket sets, and O-rings. but like you said, its been over 30 years, so its hard to get some parts, with out going to the bone yard. Yet last week I went to the local Yamaha dealer, and got 2 things for my bike. (a screw for turn signal, and a oring for the neutral sending unit).
Cool, Good luck, don't mind being wordy, I tend to be too. I am convince that some people dont' read my post, because my solution will be on page one, of a multipage response, and I feel I said that on day of the posting. (it happens)
Look for the post marked Rerun manual. its a 45meg post of the supplemental manuals. (all of them) Then on the manual page is a parts listing for the (XS400 SH) which is close enough for most of the 80+ bikes. The you can use the various Yamaha web sites for parts sourcing, (
www.boats.net, partzilla...)