its getting warm for one of two reasons
1) your finger is on it the whole time..body heat, and now psychologically you think it is hot (this happens...I did it...my wife did it...we get paranoid)
2) (more likely) it is dirty, acting as a resistor and warming up
Look for: bad contacts, rubbish springs and so on...its a "use the eyes" moment:-)
Mechanical mods do require maintenance, and this is one of those times...keep it clean, keep it performing.