I think I know the answer to this question, but thought put this out there to those that have done it:
To replace the fuel gauge gasket, is it absolutely necessary to disconnect the harness from under the tank, or is there enough slack in the wire to pull up the fuel gauge just enough to get the old gasket off and gently work the new one over top of the gauge?

 

Wow, nobody's done this or knows, huh? Guess that means I need to do it "by the book" and not risk breaking wires (not that I really need or use the fuel gauge...).

 

So, in answer to my own question (and in case anybody cares), I went ahead and I removed the wire from the retaining clip under the tank, but did not disconnect it. With the wire out of the clip there is a quite a bit of slack in the wire, so I pulled up on the fuel gauge, and it came out easily. I pushed up on the wire from the bottom of the tank while gently continuing to pull up on the gauge and found there is plenty of slack in the wire to get the gauge entirely out of its cavity. The original gasket was brittle and broken so getting that off wasn't a problem, but I did find, as per my original thoughts, that I could indeed work the new gasket over top of the gauge to replace it, whereas the manual instructions are much more involved and includes removing all tank fasteners and moving the tank back. Why? I'll never know. 5 minute job, tops, the way I did it. I actually found it easier than getting off and then working on the new fuel cap gasket...LOL

 

Thank you for this! Going to work on this today.