You can get at the focusing mechanism from the rear without removing the optics. Do this with the tube horizontal or pointing the corrector slightly upwards, not pointing down.
There is a little set screw on the side of the focusing knob, loosen it but don’t let it all the way out. The black knob will slide off.
The three button head screws on the black collar around the knob are removed next. Now the ball bearing assembly and threaded rod can slide rear wards. In the center of the threaded ro the should be a set screw and washer. It nay be necessary to thread the bearing assembly up the rod to see the. Some versions used a c clip instead. Either case, remove them. Noe unscrew the bearing assembly all the way off the threaded rod and slide thevrodvrearwards to expose as much length as possible. Clean off the old grease, I find a little GooGone citrus gel on a cloth PecPad works fantastic. Repeat as needed and then wipe dry.
Clean the inner threads of the bronze focusing shaft inside the bearing races with a cotton swab or little roll of towel and the same solvent,
For the bearin housings, there are two nested together, Imusually use WD40 to soak in between and pentetrate a bit and wipe off the excess.
Then dab a little Superlube or Napa Silglyde on the end of the threaded rod and screw the bearing assembly back,on and run up to the rear cell of the tube, Leave it a little loose. Reinstall the washer and setscrew or C clip on the end of the threaded rod. Reinstall the bearing retainer with the three screws. Don’t tighten each screw all the way initially, round robin them and try to keep the bearing centered. Snug is good but not a lot of torque.
Now put the tube front cell down and run the focuser up and down and see if it binds, if so, shift things around a little until they are free moving. Then gradually snug up the bearing retainer screws. Reinstall the knob but don’t press it all the way up against the back of the bearing or it will grate and feel rough.