Starter Problems?

[Rutteger]

Hey guys(and gals), I own a '92 Geo Tracker, 5-speed manual, 4x4 and have the following trouble:
The car will not start when it is WARM out without tapping the starter. If it is cold outside, it starts up just fine, also won't start after the car has been running a bit(assuming becuase of the warm engine) There is no clicking, and when I tap, I don't need a second person, I can just tap it, get in, and it starts. Anyone know what I need to do to fix it? I hope that I don't have to replace the starter, and because it seems to be a temperature issue, it may be the cellinoid(sp?) switch. Thanks fo you help in advance!