So my TT is going on 3 years old now, used several times a year, nothing crazy, and I am about to install my third 30 plug head. As I hold the plug in my hand, prongs facing me, the one on the left s...
A loose connection will cause the problem you have. All of the replacement 30 amp plugs I have seen are fair at best as to quality, and are hard to get a good tight connection on the wire. You may try to tighten the connection and then solder it.
Another spot is the receptical it is plugged into. If the wires are loose there it can transfer the heat to the plug.