Well there is an adaptor for where the objective thread is bigger than the sunshade thread, I'm not sure if it's now on their web site as it wasn't in the past but I have one fitted.
Whether that is the same one as you require obviously I can't say, You don't actually say whether the cover is larger or smaller than the objective
Just a thought, check that an adaptor isn't stuck on the shade (or on the scope if the cover thread is too big) it's quite hard to see, the edge is only a mil or so wide, if not phone MTC with the part no of the scope & they should sort it.
A big sidewheel is on the web site, but not the thread adaptors I've just looked.