No theres a seal on the top of the drive shaft that keeps the trans lube in the joint and the trans ,the rear is seperated by that seal and is filled on it's own . As for that mud and water in Your trans ,the mud is the old gear lube mixed with water I just got a four speed trans that was left outside for who knows how long and it to was filled with water and (mud) I filled it with a water based parts cleaner that I use and cleaned it up than filled it with some 30 wt. oil to store the trans . I think the trans fills up thru the top shifting seal when it's lift outside it's the only way it would get in . I would get some parts cleaner in the trans than run it for a few miles drain than fill with some lite oil and do the same a few times than fill with gear lube just check to make sure the seal in the top of the drive shaft is not not leaking all Your gear lube into Your rear end check the trans level it should stay the same.

Pete

1952 Chevy 3100
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