I have 2001 F150XLT 4.2 V6 has a small oil leak at the rear crankshaft seal.Can it be change with the motor still in truck by just dropping oil pan and lifting motor or do i have to pull motor and split the block?

 

If it's the rear main engine seal at the crank, you will have to pull the tranny out, and the flywheel or flexplate to get to it. One piece seal. Takes minutes to pull the seal and replace it. The rest of the day or two is spent pulling and reinstalling the tranny.

If it's the rear oil pan seal, you can try to raise the motor but you will find very limited space to get between the pan and block to clean the old gasket and sealant off and then to put on new. The other option here is drop the tranny, disconnect the exhaust, etc, and be able to lift motor high enough to be able to pull the pan over the cross member and clean surfaces of the pan and block. The rear seal is a small half round piece, the rest is sealer that has to be put on the pan and the pan to the block BEFORE it cures. Usually in minutes.

Also check that the leak isn't coming from the lower intake manifold at the back of the block. It lets oil run down the back mimicking a rear seal leak.