Doc is probably thinking of Fluid Film.
As for "shredder", I'm thinking it could be an AKA for:
3PH chipper/shredder for branches
3PH Rototiller
3PH bush hog
My guess of all being 3PH pieces of equipment, grizz may be talking about the lever to engage the PTO.
I don't have a BX but when mine is hard to engage, it's normally because of my position on the clutch pedal. If not depressed far enough, you can't engage.
Does it matter if you're in gear or neutral? Does the BX require you engage the clutch? Have you checked linkages to make sure there's no slop or loose connections?