In Episode 02 of the Quest for Perfection on the 1997 BMW E36 M3 sedan, I remove the MOMO aluminum cue-ball shift knob from the previous owner as well as the leather shift boot. We thoroughly clean and recondition the shift boot, clean the shifter area of the car, and then install the new ZHP shift knob.
Normally you pull straight up on the OEM shift knobs to remove them, but some aftermarket shift knobs like MOMO use small allen screws to attach to a shift linkage in order to be adaptable to all types of cars. If you have an aftermarket shift knob and try to simply pull it off, chances are there are allen screws that will prevent you from removing the knob. Check for screws, loosen them, and the knob should slide off. Attach the new OEM shift knob with the groove centered on the groove channel of the shift linkage. Snap it in with a hard whack and you’re good to go.
I used Trinova leather cleaner and conditioner on the leather shift boot. This is a great product and works wonders on all types of leather — I have even used it (in spite of manufacturer claims) on things like hard vinyl-like plastic trim with excellent results. Test the product on a small sample in a place that is not obvious before tackling the entire vehicle.