You can see why I suggested giving a good kicking first. Another useful tip, once you have popped out the flanges then fill the diff with oil. Pop the half shafts in if you want, but you don't need to. The BMW diff will take its proper fill of oil without it coming out the sides. I verified this by then pulling the half shafts back out ( which you have to do anyway when you build up the dedion) and no oil came out.
Filling now stops lots of faffing about later when the rear is all built up. Either make a funnel and tube up to fill it, which you will need to fill the gearbox anyway (plus a piece of dowel), or you can get for about £15 a draper large metal oil syringe (500ml) and just squirt it in.
Regards
Mark