Matt,
Wasn't sure if it was an O-ring or something made from another material, but when I got it apart, I found a small, very worn O-ring. I also scoped it out for possible replacement of the petcock assembly with a fuel bowl, which I had off an old B&S engine, but the B&S fuel bowl assembly was too corroded up to be useful. I might decide to put a small fuel filter in line, or take the fuel bowl off of my old 102, but for now everything seems to be fine. While I had it apart, I decided it was time to repair the rubbery choke cable. I had cut the housing too short before, and left a long section of the wire unsupported. Did it right this time, and worked out the outer housing length before committing to cutting the new wire.
The thought crossed my mind to start doing the hydraulic lift conversion while I had the fuel tank off and part of the dash apart, but I decided to save that for another day, probably after mowing season. When I do it, I'm going to need to work out the kinks that I already have with the linkages, put in new gaskets, etc.
Got 2 other projects in the garage to finish up anyway. First is bleeding the clutch on my Honda Shadow, the second is to get some work done on the 102.