It's difficult to tell from my end- I'd be suspicious of o-ring. It has to be a snug fit going down hole and then when gas hits it, it will swell up a bit to make a tight seal. It is 30 years old remember. These are standard buna plumbing o-rings commonly available but you need a vernier caliper to measure the diameter at bottom of groove. O-rings are sold based on ID and cross section thickeness. If you got a Suzuki dealer nearby, I try them- probably a couple bucks apiece for the correct o-ring.
this member sells o-ring kits but I'm not sure he includes the one you want;
http://www.cycleorings.com/450.html
this member sells o-ring kits but I'm not sure he includes the one you want;
http://www.cycleorings.com/450.html