The easiest way is to knock the roll pin out of the cap and then the stem assembly and screw should all come right out the bottom of the tube. Mount will fit on a drill press better this way.  Please use a new spirol pin when reassembling and note the location of the plastic washer and collar (long end down) when you reassemble. If you call into the office I'll ask they send out new roll pins N/C and mail them to you. Manuals are online here.

Call the office for any additional parts info.

If you feel it is easier you could just drill a hole in the side of the mount tub about an inch below the handle without disassembling and drive in a drive type grease zerk. I wouldn't worry about hitting acme screw, it's some very tough steel but you should be able to stop the drill.  I feel its just easier to knock the 1/4" roll pin out with a roll pin punch and clean things up.

If they don't have the zerk those parts were made around 1991. Glad they have lasted.  Yes the new magnetic handle is nice.

I hope you have the regreaseable hub caps also. Don't be afraid to pump grease in until it comes out around the seal. At the speeds these run the Timken tapered roller bearings can run with the hubs full.