Its possible to replace the large seal at the bottom where the Pitman arm is. Simply remove the pitman arm and the 4 bolts for the lower cover plate. Then tap the sides of the lower cover plate gently to get it to free and pry it off the box with a flat screw driver. Once off you can replace the large black inner oring and the bottom external seal. Keep in mind that the inner oring does most of the sealing in that area and the outter seal is just backup. And just as if you were working on an automatic trans use vasoline or trans assy lube to lube it before re-assembly.

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ASE Master Tech, L-1 30 yrs Benz and BMW Experience, Working for myself as a Mobile Technician