I tried Millers 75W 90 fully synthetic and the diff was noisier than before so I bunged in some cheapo 75W 90 (Comma I think) and it was much quieter.

Well after reading that lot I'm glad Rommel is VOR in my drive way. Otherwise who knows what challenge/s the P38 god / goddess would put my way this time on my trip to Limoges and back 😆

You should be OK. Things come in threes and we've had 3......

Hi Dave, I just use EP90. My local motor factors sell Granville everything, and I decided that my 20 y.o. vehicle doesn't really warrant high end branded lubricants. My eyes glazed over at the synthetic gear oil recommendation - a bridge too far IMHO
Re Loctite I have blue 243 that I use 99 pc of the time (medium strength), then I have red 270 (for parts that do not require disassembly) and green 648 (retaining compound, for things that really, really do not require disassembly). I'm frightened to use the 648 - it's actually designed to apply to the half shaft/ diff or half shaft/drive flange to stop any clunking when drive is taken up so seriously heavy duty. I didn't use it in the end, as it turned out it was the diff itself that needed replacing, and the half shafts were fine.
I noticed (on the larger bolts especially) that the loctite needs to be fresh when it's bolted up, else it can be hard work (feels as if there's a crossed thread), which will also throw out the torquing-up process.