I've done it on a BJ8. It was a pain pulling the pittman arm but, after that, seal replacement was typical. You have to work around the rocker shaft; I used foot-long lengths of 1/8" rod flattened into small, hooked screwdrivers to work around it. The replacement seal should be thick, about 3/8" IIRC, and the ones I've seen were silver metal. Some vendors sell a thinner seal, which won't work well if at all--stacking a couple works for some--and the ones I've seen were painted green.
Regarding pulling the pittman, later whilst working on my BN2's box it occurred to me that it might work, and if it did, it would be easier to pull the mounting bolts for the box, loosen the bracket under the fascia, and rotate the whole assembly 90deg counter-clockwise to get to the pittman and seal (after you get the linkage off, of course).