Assuming that actually works, it very well may work all the way back to 1968 models, as the early caps (without a lock) fit on the models up through 1976. Please post your results as this will be a good bit of info for salvaging those old caps!

I got the gasket from eBay, and it seems to be a good fit. It fits snug in the center and the outside edge seems to run right up to the edge of the cap. I’ll ride the bike to work tomorrow just to make sure it doesn’t leak.

rover.ebay.com/rover/0/0/0?mpre=https%3A...2Fitm%2F372882711713

You can buy the gasket in 10 packs too... $15 I think with free shipping... going to order mine off Amazon

I too looked into buying one for my DT250C from J&P cycles but I felt the same as smd3 I did and also could not stomach the $7.99 shipping for the same reasons as smd3.
I followed in his foot steps and bought the one on eBay they ranged from like his link $1.99 to $21.00 for the same part number.

I received mine today as well, as mentioned above it does fit tight in the center, outside diameter seems ok, but appears to be only about half as thick as the original, I didn’t feel comfortable using it by itself, so I left the original hardened one in place and put the new one on top of it, after putting the gas cap on and off a few times it seems to have settled in nicely, tomorrow I’ll fill up the tank and go riding to see if I still get seepage around the cap.

I had bought a sheet of 1/8” thick Buna-n from amazon as well thinking I could cut out a dozen or so from one sheet but I traced out the old gasket and wasn’t able to get smooth circular cuts. I have seen a few gasket cutting tools or punches that will cut nice smooth circular gaskets in 1/8” rubber but then you get into lots more money for a tool that will probably only be used once.

All in all the eBay gasket will probably work fine if you can layer it over your existing gasket or possibly buying two and doubling up if you don’t have the original gasket on the gas cap.

Mine seems to fit pretty snug and seemed about as thick as the original. Of course my original was pretty dry.

I bought this buna-n and it didn’t work for me. It got all weird and deformed.
Buna-N Sheet Gasket, Black, 1/16"... www.amazon.com/dp/B0075DXMAK?ref=ppx_pop_mob_ap_share

When I installed the new gasket on the cap by itself the cap seemed to turn a little to easy, like it did with the original worn out gasket and it felt like it wouldn’t seal, so I installed the old gasket back on and the new one over the old one for a double gasket seal, seems to turn and tighten down with a positive feel. I haven’t had a chance to test mine for seepage, I will try tomorrow and lay the bike on the side to see if it leaks, have you tested yours for leaks?