Went away to exmoor for the easter weekend and had an amazing first trip, completely missing the rain!
Got the garage to have a look this week, and they reckon the leak is from a seal inside the gear box. He says it'll cost hundreds to sort properly (rebuild), but should be fine if i check it every couple of months and top up whenever necessary. He also said there was no nasty lumps of metal on the magnet when he removed the drain plug, so sounds like no damage done, and he didn't charge me a penny
I have no clue about this, but does what the mechanic says sound about right?