[MetalMan]

Well, without knowing how hot things got we don't know if there's a problem or not.

Typically 140 deg. won't let you hold on for more than about 5sec. (depending on your tolerance to heat), so assuming that's the case for you then your setup is fine. The best thing to do would be to pick up a infrared temperature gauge like the Duratrax Flashpoint ($25) so we don't have to make any guesses.

If you were to solder on a cap, you'd want it to be as close to the ESC as possible. If you have a good soldering iron you can attempt to solder onto the ESC, more specifically the cap would be soldered right under the battery leads on the circuit board (to positive and negative).