I recently replaced the 20 year old R/R on my Curvy with a Mosfet one as it the Regulator side went high and took out my Rev counter and damaged the battery.With a bit of Electronic Trickery I've managed to repair the Tachometer for now
Here's the chronicle of the R/R job,
http://puttingoutfires.x10host.com/M...sfetUniRR.html
Old style R/Rs can get very very hot and even more so as they age.