I suspect part of your question is, WHICH drain plugs need copper washers? The only one I can think had one is the engine oil drain.
Which fluids? Many people on this Forum like Shell Rotella for diesels. Widely available including Walmart & Kmart at about $14.00 per gallon.
These Rover manual transmissions originally called for automatic transmission fluid. Current opinion is modern ATF isn't the same as it was 20 years ago. As already mentioned, Red Line MTL is widely used on this Forum. (Unlike Rotella, it's expensive, I think I paid $15 per bottle.) DON'T use 'gear lube' in Defender manual transmissions.
For the other fluids, use your favorite brand, synthetic or not.
Originally Posted by LRColorado
Can you also tell me which drain plugs need copper washers?
Can I go to the local auto parts store to buy them or do they need to be specific to my vehicle?