slightly OT

Common or garden EP90. Don't bother with synthetic, they leak often enough that it's a wasted expense, they survive fine on EP90, and you'll get water in it whilst fording (even with the best of care) and have to chuck it out anyway.

The diffs in my Dad's Series IIa are still quiet, the gearbox has had one rebuild about 100K miles ago, and the transfer box is getting well noisy now but it's done ~340K miles on EP90 so you should be right for the foreseeable future.

I've got some mega expensive synthetic stuff (gift from the supplier) in my Series gearbox (in the hope it'll cope better with the Holden 6 cylinder's 170HP in front of it) but the first time I have to change it I'll go back to the cheap stuff as I don't think it makes much difference.

You need to use a solvent to clean it - carefully and gently. Do not overwet it, then use blotting paper to gradually remove the musty stuff. Try Isopropanol (isopropyl alcohol), Benzene (a bit of a nasty one, best avoided) or Acetone. Usual caveats about not taking a lungful of anything, suitable ventilation, protective eye-wear.

Use an old style (but not used) sanitary towel on large documents, use a lint-free cloth to apply solvent, etc...

or... go buy a new manual

or live with the one you have ;-)