I will assume that your starter 'run on' is due to the welded contacts on you starter switch. If not, then you need to address that issue before you roll out of shop.
On your other issue of shorted brushes. I don't understand how your starter turns if your brushes are grounded. Grounded brushes would not put any voltage across the starter, therefor it would not spin. Is your testing procedure correct? Starter windings present very little resistance to an ohmmeter. Is is possible to pull the starter and have it checked out by a trusted shop?
