Inside the end for the power cable posts will be the brushes. It's a good bit of fun getting them back in once you've opened it up and are reassembling. But the noise is one of two things, either the bearing(s), can't remember if there's one on the brush side, or the starter bendix. If the bearing in the starter is going bad it will slow the cranking speed and draw excessive current which will burn things out like the brushes and the wire they're attached to, possibly the solenoid too. If it's the bendix, it's because it's starting to seize and as you heat it up you're introducing expansion into a part that has already lost clearance because of rust and corrosion from sitting further binding it up. Usually the early telltale signs are a sort of squeally groany tone after the starts and the bendix is trying to retract to it's disengaged position, or you get the infamous buzz from the starter spinning but no engagement with the motor. After multiple tries the centrifugal force finally breaks the seize and you get engine engagement. Sometimes it'll let you go the season like that, sometimes it'll let you get a few starts before it finally seizes solidly.
When taking apart the starter, get some 400 or higher grit Emery cloth and polish where the brushes contact the core of the starter, check that the brushes have at least 3/8" of material to keep the springs well loaded, if they don't then you'll need a brush kit. Once they get down to 1/4" or less they'll pull out with the rotation of the starter and jam up. In the barrel of the starter there are alignment slots for the brush plate, it is only supposed to go on one way, that's why your bolts are offset from a straight line, because either the plate was jammed together or the tabs on it are broken off. But you'll definitely see there's only one way they can go together. If I recall there should also be a few thin lines cast into the outer body of the starter to help with aligning it all. But they're a very basic concept, remove the nut, lock washer and insulator off the post, pull the barrel apart in three pieces, don't lose the square shaped rubber insulator on the post that seals it from the body, replace orings if nicked, stretched or obviously if they break, new bearings if needed, polish the commutator core, blow out the dust, reinstall after a bench test. If the bendix is going bad, just replace it with a new one. It's not worth trying to clean them up and recondition them. They will leave you stranded.
