I'm not a Transmission rebuilder by trade but (I did stay at a Holiday inn last night) have paid to have some work done on that part of the trans.
The left axle/drive shaft has to be removed to gain access to the left cover on the trans. Under that cover are the misc. valves and switches that can be replaced.
I paid $600.00 the last time i needed any work done in there.
Theres quite a bit of labor to gain access, left wheel, brakes, spindle and axle need to be removed, if I recall correctly.
That was at a shop labor rate of $72.00/hour