Cassette motor lubricant; factory reccomended type ?

I collect lots of different boomboxes and work on them for my own enjoyment. I have found some of the cass. motors sound a little dry on lube. I haven't taken a motor apart yet. I also noticed some of the nice older ones have a little oil hole on the back of the motor. I want to know if you can tell me what is the Best way to lube the motor bearings and what is the correct type of lubricant recommended for longevity. Thanks !