Safari 89 starter trouble

Hi there,
I own a 89 safari with the 4.3 liter engine.
This week my starter seems to have died.
I started the engine, the starter engaged and gave me a weird noise (the noise mechanicle thing make before the die) at the moment the engine started. I drove home withut any trouble.
At home I've tried to start again, but the starter didn't turn. The lights on the dasboard went dim, but nothing else. The battery seemed ok though.
Ive replaced the starter with a remanufacterd starter and it worked fine for 1 day. Yesterday, it didn't do anything anymore. The starter was really warm.
I've released the screws of the starter as far as possible to get it away from the flywheel and the starter runs like a charm when I turned the key for a sec. I could also turn the flywheel by hand (hard, but possible) so the engine doesn't seem jammed.
I tightend the screws from the starter again and the engine started like a charm. After driving home I switched off the engine and tried to start again and it didn't do anything. The same thing happened as the old starter. (dashboard lights go dim, but the starter doesn't turn)
Any suggestions on things to check before I take the starter back to the store to have it replaced again?

Update:
I've opened up the starter and the bracket of one of the brushes has cracks. It seems as if it is almost broken off. I'll go back to the store where I bought the starter to have it replaced.

With kind regards,
Rob

Well, new doesn't mean it's works - that's what warrantees are for....
A suggestion: maybe it's misaligned, and staying engaged to the flywheel. That would definately screw things up, like crack the brush, and overheat it.
How would I check that? check for dirt at the mounting flange, check for squareness at the mount, just before the bolts are tight, check for some play, that it's not jammed into the flywheel. I've read about shimming starters, but I'm not sure how common it is.

you're right, but:
I went to the store and the tested the starter. No problems.
Unfortunatly shimming this starter is horrible. I don't seem to be able to get the starter to connect to the flywheel manually. Getting really frustrated with this problem I made a shimmer myself and installed it. Now the starter works evrytime. I'm guess it was to close to the flywheel and therefor it could align properly. I guess if the starter is to far away from the flywheel I'll hear that in time.
For now at least the thing is working. I'll check the flywheel from time to time to make sure the starter is not to far away and therefor damaging the flywheel.
I've had it with car-repairs!