Quite a common problem, but i have had success with helicoiling(thread insert) them, but gotta dismantle to do it. must be very careful to clean out ALL swarf, as it damages pump valves.Take the banjo bolt in to your local spare parts place, and they should be able to supply you with a kit to do the job. It will be stronger than the origional threads.
P.S. this will also work with damaged diff and gearbox threads
Hope that helps