My ST4000+ was completly dry inside - the ball race
couldn't be turned on the drive rod screw (it should fall and rotate under its own weight). I've attached my notes. I must stress that Raymarine
advise that "there are no User Servicable parts
inside" the push rod. But if one has to take it apart (I did - I was miles from nowhere 1/3 of my way into a trip around Aus with no working autopilot
. A new one was eventually flown in from England) then my notes might help.
The hard bit is getting the viscosity of the lubrication right - I would suggest as light as possible.
To replace the motor, one does not have to take it all apart - only the back section near the pivot. A previous post, enclosing the manual, shows it well. Cheers,