Shifting problem with 833

I agree with Ace on the oil especially with the 833's, start out with a good new oil. It sounds like your clutch freeplay is set correctly at 1/2" at the peddle. Could be a number or other problems such as shifter linkages are in need of adjustment or the brass bushing in the flywheel is siezing to the tranny input shaft causing it to not disengage from the engine when the clutch is disengaged.
Side note, if you turn one wheel and the other turns in the same direction, with the rear up in the air, then it is a posi or limited slip or shur grip and I never use additives in the tranny oil only in the rear end if it's a posi.

Terry R