The differences are whether you have hydraulic front wheel assist or not and whether the pump has a serial number plate or not. The original pumps never had a serial plate. If it has been replaced, it might have a serial plate. A 2wd 4020 with original pump with no serial number plate uses RE29103 kit. PFWD front axle needs Re29104. If you have serial plate, with no PFWD, you need RE29107, and the PFWD with serial plate uses RE29108 kit. All of the kits require ordering a RE28790 seal for the main shaft seal. It is not included.
