If everything is lose perhaps a small pry bar or other suitable tool coul be used to persuade the stepper mounting plate to seperate. It may just be a tight fit on the dowels and it sometimes takes gentle prying at each end to get them apart. If the gap is very small I have even had good luck getting things started with a rigid putty knife, and then using a pry bar to finish up. Make sure all fasteners are remove and there is nothing holding it in place before trying to pry it apart. Just curious, but why do you need to seperate the parts to begin with? Modifications?