Alan, why not strip everything down? These machines are simple enough, the manual is good and a wealth of help is available here. If the previous owner was daft enough to use grease, rather than read the manual, who knows what else he's done? You need to find out, and you'll learn a lot about your machine.
I bought an Emco FB2 milling machine, also grease-lubricated by the idiot previous owner. He had put washers under the table logitudinal feed nut. What??? Obviously had no idea of how to align a feedscrew with its support bracket.
Having said all this, provided the grease hasn't hardened and blocked the oil passages, it probably hasn't done much harm. The risk is that chips and crud aren't washed out from the slideway bearing surfaces by frequent oiling – grease 'hangs around', so doesn't seem to need replenishing so often (by the misguided).