Not sure if this is a common prob but I just had the nut under my seat pin/bolt came loose.
I am sure you all know its tack welded to the inside of the frame at 3 opposing corners.
I am thinking the mouse commune that sprung up inside the frame during its 20 year hibernation created the moisture (breath vapor, piss, honta virus, etc.) required to rust the bolt to the nut stronger than the welding.
Normally it would be no big deal. I would just reach under there and hold the nut with a wrench while I tightened the bolt on top.
The rub is that I have a rack that is held down by that seat post bolt.
You can't get the tank out with the bracket on and you can't get the bracket off unless you are able to reach in and hold the nut.
Get my problem?
I don't see how it would be possible to reweld it.
For the time being I am just going to rock it sans bracket/rack but eventually I would like to get it back to how it is supposed to be.