I just cleaned up a real nasty example in a Golden Tee. This is a Betson, 4 screws in the bottom hold it together.
Full of beer and crud, and barely rolling.

Oil bath for the bearings and cleaned the rollers with metal polish.

Scrubbed all the funk out of the housing with hot water and dish detergent

Scrubbed the ball up too.

Putting it back together.

Ready to go back in, worked like new.

They sell bearing and roller kits for these as well, if you run into one thats really worn. If they're that bad, chances are it's worth just buying a whole new unit.