Sorry I am late here, I have experience repairing Davis Standard, Mazak, and American Eagle lathes and Mills. Most common repairs include clutch pack tensions and replacement, and replacing the various roll pins. Next to that stoning the "ways" and replacing the "gibs" are about all you want to tackle. Everything else requires either shaft or gear replacement, or in extreme cases replacement of the housings.
Change the oil on at least an annual basis, and keep the ways oiler topped off.