Hi
It sounds like the brushes have worn out on the motor, which can happen if the belt has not been lubricated often enough, this produces a lot more friction and the motor works harder and therefore wears out the brushes sooner due to arcing and general wear and tear. I am also looking for some brushes for a TR2 which has worn out the brushes in the motor and this exibited the same symtoms as yours has, sparks and smell... also not always working.
To find out remove the cover over the motor after you unplug it from the mains, then look at the motor and it will have 2 plastic sloted covers oposite each other on the motor, unscrew these and remove the metal sprung brushes and inspect them, if one or both are worn down then this is your problem, the next problem is trying to obtain replacements... good luck and let me know at andymcj@hotmail.com if you have any luck.
AndyMcJ, April 2008