I bought a BMW e39 with a bad transmission (ZF 5HP18). I bought another one in a junk yard and I plan to rebuild myself the one that came with the car and keep it as a spare. My question is: after I do the rebuild and put together the old transmission it will be dry without ATF how do I store it (for years)to avoid corrosion on the inside?
welcome on this site.
Good luck with rebuilding the transmission, this is one of the bigger challenges in car maintenance.
You need to store the transmission with ATF inside in a clean dark place with constant temperature. Do not overfill the transmission. Ideally the gearbox is wraped with oil soaked paper/rags