OK! I've got the Yamaha part # for the copper/asbestos exhaust seal that I installed on my AVL 500cc engine:
it is a YAMAHA #, lcx146130000.
My local Yamaha dealer, "Yamaha Jack's" in Ellensburg, WA, just happened to have ONE of the seals ---that turned out to fit the RE!!!(it was a special order that fizzled--what good luck for me).
This Yamaha dealer will know exactly what to order!!!
For the techno-geeks among us, I researched the I'net and discovered that a DISTRIBUTOR(not a dealer) called K and L distributes a VAST assortment of these and other exhaust sealing rings/gaskets. Their online catalog even gives ID, OD, and thickness for each. There actually exist other copper sealing gaskets in their catalog, with slightly varying ID, OD, and thickness!!! Take your pick!
I note that K and L sells these "ten to a pack". Hopefully Yamaha parts distribution system will break these packs apart to sell me the ONE MORE that I ordered from Yamaha Jack today!....
As for the recommendation regarding Aircraft Spruce as a source of copper crush washers.....the Forum-provided Spruce chart tells me, anyway, that they are the traditional CIRCULAR CROSS SECTION copper sealing gaskets!!!!!!!IMHO, the OD/ ID/ thickness geometry of the Spruce gaskets are NOT the same as the exhaust seals that I have referred to!! (I would describe the Yamaha gasket cross-section as an "over-stuffed SQUARE--about 4-5 mm of a side). To me, then, a single "Spruce" copper gasket will NOT be thick enough to seal at all well. Being circular in cross section, they will NOT
provide much sealing contact AREA, even if "crushed" a whole lot. The temptation to use 2 or 3 of the circular "Spruce" gaskets will only make more durability and sealing problems arise(IMHO).
Finally, I will admit that a $14 Yamaha exhaust gasket is way too expensive compared to the ~$1.00 or so for the "Spruce" gasket.
Ellensburg