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Well, thanks so far fellas. A few comebacks:
TWR - Cheers bud, i have checked a few times now and the dewdrop is from the bottom of the gearbox (not where the gearbox sump plug is) so i don't think there's a need for further confirmation. There was a washer on both, of which I replaced, both remain dry.
Toureman, cheers i will take a look.
AlBags, thanks for the thorough response; I don't think I have overtightened the plugs and your comments about the outshaft/mainshaft/NS seal is above my mechanical comprehension! I can't check the transmission level, only fill it (with a bit of hosepipe) til it overflows into a pan, so I guess there's enough? Cambelt was changed (according to the somewhat dubious service history) 20,000 miles ago.
Thanks guys, appreciate the time you took to respond.