when you go out to change it out (or you can check it out sooner) check the wiring , some of it might have gotten wet over the years and now has a poor connection.
That sounds just like like brushes to me.
Bet they are worn thin and barely making contact... usually only a couple bucks to replace.
Glad to hear you are up and runing again, tvropro, man cannot live on Ku-band alone!
If you can't repair that Saginaw don't throw it away, if that sucker is built like mine you can always use it to drive tent stakes, or something.
Most independently owned hardware stores (the old "if we ain't got it you don't need it" stores) carry them - in various sizes.
Usually they'll have drawers full of them. If you can't find some that fit exactly, you can usually get pretty close and do a little 'engineering' on the new brushes to make them fit.
We have a local hw store where I've done this quite often.
Also, I believe McMaster-Carr and Grainger carry them.
Iif the commutator looks ok, leave it alone. You're supposed to undercut the mica segment to segment insulators after turning.
Sanding down brushes by placing a piece of sandpaper on a flat surface is easy and fast. Make sure the curved end of the brush that mates with the comm goes back in the right orientation.
If the motor has bushings, put a couple of drops of light weight oil on the felt pads. If it has bearings, check and replace if needed.