If you have a parts vendor that is willing to work with you on the declarations (low $$ value), then maybe parts are your best solution.
The duty game brings back memories as I got caught out a number of times when living in Australia and importing parts, never did figure how they do the duty calculation! I was working in S. America and actually bringing most of it back in my luggage at one point, even a full carbon exhaust system for my Ducati of the time. Trick was to take back a couple pounds of Coffee and declare them, then they didn't touch the rest of your luggage on the assumption you were being honest
Then they installed those scanners that all arriving luggage had to go through too and my game was over....I'm sure you must have competenmt TIG welders there to fix the crack. Unfortunately the ZF is next to worthless in it's current state, so you wouldn't get much back on it. Fixing it is still probably the best option by the sounds of it.
Good luck,
Julian