Another meathod simular to Dave's is to punch a hole in the seal casing with a sharp screwdriver and lever pry it out.
But the important part is to index the flange nut before dis-assembly to the pinion shaft so that it reassembles to the same spec.
There is a crush bushing on the shaft that is factory set and if it is crushed [ tightened] any further the differential gear mesh will be wrong [ NO GOOD AT ALL]