I'll tell you four things about this subject...
One... the problematic side with this design is typically the passenger-side, due to the exhaust-system passing right close to it. Too much hot/cold action going on there, allows moisture in when the nut expands before that threaded end of the radius arm has a chance to heat up as much as the nut. I know from experience.
Two... I am sure the heat helps to break down the rubber in the factory bushing.
Three... Often when this bushing gets screwed, it is the inside of the bushing that is affected. Without disassembling it, it appears fine externally. If you put a pry-bar on it with the suspension loaded, it may be a different story.
Four... When one of these bushings is screwed, you will notice what you percieve to be a steering alignment problem... typically holding the wheel at about 11 o' clock while driving, and having to slightly correct while braking or accelerating. That is the biggest tell-tale sign. The reason for this is because your wheelbase actually changes on one side of the vehicle more than the other, which causes a rapid change in alignment briefly, and it settles when driving at a constant rate of speed.
This happens because the inside of the bushing is no longer holding onto the radius-arm firmly.
