If you are looking to rebuild your Massey Ferguson MF 12 Hydrostaic transmission, you will need to acquire the bearings, bushings, seals, and gaskets for the transmission. You will also need to have the proper tools for disassembling and reassembling the transmission. Once you have these components and tools, you will need to disassemble the transmission. After you have taken the old components out, you will need to inspect the various parts for wear and tear and make any necessary replacements. Once you have made all the replacements, you will need to reassemble the transmission by following the instructions in the service manual. Once reassembled, you can then fill the transmission with the proper lubricant and test the transmission by running it through the gears.