Starter issues

My two year old starter is playing up. I took it out
Yesterday gave it a good clean and grease, filed the brushes and reassembled. It's not even clicking once, just dims the dash lights. Any ideas?

Crappy earth somewhere...........battery to chassis/body, chassis to engine/gearbox??

Or crappy main feed to starter??

Petrol or diesel?
You could check the starter on a bench with a battery and some jump leads (be careful - it will kick) or you can try connecting the battery to the starter in situ with a jump lead (DON'T short it to the chassis!)
Could be the starter's knacked or the commutator is full of crud (copper dust between the commutator segments shorting out the brushes). Might be a burgered solenoid. Could just be poor contacts. Might even be a ferked battery.

I had it all apart to no avail, whacked a knackered old starter on there for now, works a treat