Large O ring on dizzy? Rubber or other

thanks for all the comments. Update: So I took the old Oring down to Oreilys, the Dorman selection had 1 opened pack of Misc Orings, supposed to be a 12 pack of assorted, there were 4. There was also a special "Distributor" package with 6 oRings, some black and some Tan. Those were too small. So I went to the counter to complain about the lack of Oring selection, when he pulled out a red case , opened it and there was a nicely laid out selection of Orings. I found the right one (a little thinner than what I had, but the right size), he rang me up $2.20...for 1 oRing. Installed and no leaks.