Christy,
They're both the same type of controller. There are little carbon disks inside the large housings. The grey one on the right is "I think" the newer one.
The one on the left has been way too hot. I'd tear it down and clean the insides of carbon deposit and make sure the disks weren't broken or missing, then very carefully clean them too. They are very fragile.
ArcaicArcane has a dandy tutorial about those things here: {
http://www.archaicarcane.com/singerattheraces/ }
And some more here: {
http://www.archaicarcane.com/what-a-pile-of/ }.
The wiring on the brown one needs checked and probably replaced too.
If you haven't done these things already.
Joe