Look at where I'm coming from: if you replaced your throwout bearing with a solid ring of steel, your clutch would still operate normally. Meaning it would engage / disengage fine. There would be nothing to cause it to bind or hold the clutch or slip the clutch. It would just make a ton of noise, heat, vibration, and eventual failure, but it would engage and disengage the clutch the same way. This is why i think your problem lies elsewhere, if I understand your problem correctly.

That bellhousing can get filled up with muck pretty easily. Have you thought of drilling a hole and mounting a garden hose fitting to it? I've seen that done on frames before. You hook up your hose when your done mudding and blow out the mud. Not sure if that would compromise the bell though. Budbuilt toyota frames come with those fittings for easy cleaning.