I also have a 6 bolt box which is leaking, when at eastnor recently, I talked to the guy on the ADWEST stand and he told me that all 200 Tdi land rovers came out off the production line with a 4 bolt adwest box.
My leaking gemmer 6 bolter looked like a replacement box anyway as it was (is) a vivid bright green colour, a search through the posts sugests that 6 bolt gemmer boxes are a cheaper replacement for what should have been a 4 bolt adwest box.
I don't think that changing the pipework around would be a big job.