I have done a bunch of mine, and paid a guy to do one - never again! (Orange is orange, right?)
Anyway, there are a mess of fine details as to seal direction and such I found on reassembly. When I looked carefully enough in parts diagrams and manuals I could see a faint line (on blowup) or text to guide me. It would be very easy on disassembly to let a coaxial part fall left instead of right and then repeat the error on multiple reassemblies.
Also, some BH circuits have overloads in the controls in case tractor moves with BH engaged (say in the dirt). Perhaps one has never operated or got rusted stuck.