that would do nicely - as the tranny lives under the car anyways the cosmolene would protect it - Do you have any arms dealers in Multan? - ask them for it.
after blasting it I would carefully scrub it down with a very soft cleaner (citrus based) and then remove the bolts and galvanise them golden again, install them back and apply your cosmolene - voila brand new transmission case.
btw that should be standard practice anyway, I just tie up all nuts and bolts into wire and bag them - hand over for galvanising and end up with new looking bolts and nuts - adds considerable eye candy to the job. And being a german vehicle it sports Kamax fasteners - all the better.
did you ever find the correct lube for your steering gearbox?