question for transmission 2001 ford escape 4x4

[ms clueless]

well i just bought a used transmission and not to mention this is the third mechanic shop i'v had my truck at n e ways the mechanic said a part was missing which is the 4x4 which i think is the transfer case .He said he put the trans in and then added the trans fluid and noticed it leaking out i guess this part he needs is what keeps the trans fluid in side the transmission ,and makes all four wheels work .Ok the 2nd ? is isnt this part included when i bought the used transmission?What should i do go back to the place where i purchased the transmission and ask them where the 4x4 transfer case is if this is what it even is?please help thanks!!!

[cam 540]

They probably sold you a trans for a 2 wheel drive escape. Just curious what did you pay for the used trans because I might have to buy one myself?