The seal is no biggie, if you are careful you didn't need to upset the crush spacer.
A big 3/4 drive rattle gun makes removing the nut easy if you can find one.
Quaility of the replacement seal is important.......genuine landrover double lip ones work best if you can find one as the extra lip keeps the mud and dust out with the outer lip shaped to cup into behind the drive flange oil slinger.
I locktite the both the flange nut and drive splines on the drive flange.
I do this because you need to tighten up the flange nut slightly under that needed to crush the crush spacer....ie slight less than it was before and I do the drive flange splines as wear is normally present and the splines will move tending to loosen the flange nut and also allow oil to travel down the splines from the diff and to the out side world.
The dis advantage of loctiting the drive flange splines is you will need a good puller to remove it in the future.
Every thing to do with tailshafts and drive flanges/diff is very important with a 101 because of the almost 6 to one diff reduction meaning all this stuff is spining a lot harder than normal for modern traffic.
The 101 front tailshaft grumble and vibs also tends to loosen things too.
The diff breather needs to be at minimum to have its holes in the banjo fitting of it drilled out larger.
The standard breather banjo fitted has a extremely small hole in it, and one small flake of condensation corrosion rust from inside the diff will block it leading to blown hub oil seals and diff drive flange seals.
On my 101 I have done away with the breather banjos all together and used a Festo swivelling connector straight into the diff housing.

