How do I check a used brushless motor I just recieved?

[Rivermaxx]

I just got a used real neu 1515 1.5 d off ebay and I was wondering how to check it. It looks a little worse for wear and I just want to check it out. I noticed the resistance on the magnet definitely is not as much as my castle 1515 1y but I don't know if that even matters. I would like to freshen it up with some new bearings. I also noticed that it has bigger screws (3.5mm or 4mm) than the 3mm the castle accepts, is that normal? Is there a way to check the resistance on the windings or something & what should it be?.