Mine aren't sticky (yet?), but the general problem with sticky knobs is often addressed by using isopropyl alcohol. Using a cloth and maybe a toothbrush with the alcohol should do the trick. The knobs Can also be soaked in the alcohol.
There is no need to open the MxB; you can pull the knobs straight off. It may take some a little force for the round knobs. To avoid damaging anything, be sure to pull them straight off, not at an angle. You can use some leverage against the panel or a string under the knobs, but I find I can pull them off by hand. Be sure to protect the panel if you apply force against it. There are even special knob pulling tools, but that shouldn't be necessary.