Cheers for the replies guys 
Rocket that’s a good idea if the cap isn’t too tight, may give that a whirl. Otherwise I may have to buy BarKer some beers and borrow the socket.
TB – I’m pretty sure it was just dirt that got in the seal and caused the leak, oil is cheap so I’ll top it up first. If it leaks again I’ll get a new seal and replace it.
Filling the oil from the top with a syringe is only good if I can get the cap off. Because the ways the forks are designed you have to fill too the very top and actuate the fork a few times then remove the oil down to the required height.
I might set the oil a little lower than whatever the left one (good one) is currently at. Just need to find the time to do it before Coffs now.