dsmess,

The shop should have machined the commutator or at least sanded it and then checked the armature with a growler. That's a magnetic device that tests for an open or short in the armature.

If one of the segments of the armature is open and that section stops directly under the brush, the solonoid won't work because no current will go thru the pick coil. That's one way the problem can be intermittent.

I had an old Ford many years ago that had an open segment in the armature. Every once in a while, the starter wouldn't work and I had to move the armature with a screwdriver to get the car started. I was a teenager then and didn't have enough money to replace the starter, so had to put up with it.

The pick coil pulls a lot of current but only for an instant until the solonoid moves and closes the contacts that energize the starter. The lower current hold coil keeps the pinion gear engaged in the ring gear and the starter cranks the engine until the key is released. And that's the way it works.

P E H