RE: TD5 Defender - Problem changing from 1st to 2nd when engine is cold
Take the level/filler plug out while the car is on flat level ground - you should get a very small dribble of oil from the filler hole. If not, put some oil in it until you do. If it gushes out like mad, either the previous owner overfilled it or it's been wading and you've got some water ingress (oil floats on water, so the water won't be evident from the filler plug, only the drain plug) - either way change the gearbox oil.
Correct oil for the TD5 R380 is MTF94. This can be a little hard to come by but LR Dealers will stock it or an equivalent - the service interval is 18,000 miles if memory serves so it's well worth paying the extra for the right stuff.
UNDER NO CIRCUMSTANCES put EP90 or EPx80/90 gear oils (that's the stuff that goes into the transfer box and axles)into either the LT77 or R380 gearboxes - it's way too thick and cannot be pumped around the gearbox.
If you really can't get hold of the MTF94 then a good quality ATF to Dexron III or higher will do the job - but halve the service interval and change it for the MTF94 as soon as you can get it.