You know it occurs to me that there really is no mechanical need for the mirror and baffle tube to ever touch, and in fact, its probably a good idea that they do not. Tolerances can be tight enough that they are close fitting without touching.
There are two better solutions, IMO.
Something like the clement focuser, but internally. Properly supporting the mirror from the back, a stable system made to focus the mirror along multiple equidistant points instead of just one, where the focus knob is.
Lock the mirror down and focus externally, but build the tube with this in mind so that the external focuser doesn't add anything to the focal length as well as eat up all the back focus.
There are certainly a lot of ways to move the mirror. Doing it with flexures can certainly work (as one CN participant has shown) but it tends to me a more complicated solution. I think that the slider on the baffle tube is actually a pretty good approach, but it needs to be implemented better than the way Celestron has done it. Focusing by moving the primary requires pretty tight tolerances and/or a clever design. There are certainly some significant advantages to focusing this way. If you move the primary by x, the image moves by xm^2, where m is the optical magnification. That makes it very easy to accommodate a wide range of back focal distances with only a little bit of mirror movement. That means that for a typical SCT with m = 5, you only have to move the primary by 1" to shift the focus position by 25"! The optical magnification translates mirror tilt linearly into lateral shift at the focal plane. That means that a 1 arc-min tilt of the primary becomes a 5 arc-min tilt at the output (for m=5). So, the mechanics have to be very tightly controlled (as we have been saying.) Simply greasing the slider tube will not fix the problem--no matter how thick the grease is. There is also no way to "float" the slider tube on the baffle so that they don't touch--nor would that approach solve the focus shift problem. I think that there are basically two improvements that would completely fix the "greased pole" focusing system:
1) Zero clearance the slider tube. That could be done in a number of ways but as a retro-fix, the nylon screw idea seems quite good.
2) Rearrange the focus screw so that the slider tube is loaded symmetrically about the central axis of the baffle tube. In the Celestron design the focus screw is offset from the center and that imparts a tilt moment on the mirror. It would be relatively simple to implement a screw driven kinematic lever arm that would impart zero tilt moment on the mirror support plate. I haven't looked at the space behind the mirror to see if there is enough room to implement a retrofit of this sort--maybe, maybe not. This is something that Celestron could certainly implement with only a minor redesign.