Double check connections ?
With alternators the usual suspects are brushes and their contact rings, voltage regulator, and rectifier. How to check/repair alternators on you tube. This does mean removal and opening it up.
Depending on how you get on, it might pay you to break it, engine alone with ancilleries/rads is worth 1k, check out defender 200 tdi engine parts prices on ebay etc.
Galv chassis must be worth the same.
Daft things like roof lining are worth money.
Ah okay, i only asked as I once had this with my d2 parked in certain places it would not unlock and sometimes crank and not start, push it a few yards and it would be back to normal.
Get yourself some brake cleaner, clean it up then see what is going on.
If you wipe that oil drip off the oil cooler hose, is there a small hole in the steel ferrel?