If its the Allen screw, I ended up going to Aldi and buying an air gun at a tenner. Put a piece of broom handle down inside to jam the lower pipe (part 51440-393-003) and stuck it in a vise. The broom handle was carved down to locate properly, make sure you do not distort the lower pipe as it carries a nylon oil restrictor ring. One came undone immediately, the other wouldn't shift and damaged my hex socket. Finally drilled the head of the screw off, took the fork apart and stuck the remnants of the screw shank in the vise and undid it that way