Outer Limits 4x4 Board

I'm replacing the rear input seal on my Toyota PTO winch. I've removed the 4 bolts holding the end plate to the gearbox, but it still doesnt want to shift. I'm guessing that its held in place by an old decayed gasket and years of road grime. Can anyone tell me otherwise?

I've exposed the join with a scraper and given it a soak in bolt-off. Time wil tell I guess.

Cheers
Craig