Well that was two hours of pure fun - NOT !!
Couldn't get any real purchase on the filler hex bolt with the air box loose but still in the way. So off with all the front plastic, all bolts out of top cross member and swung it out enough to remove the air box.
Now we have good access to the filler plug but will it move - not a chance and worried that the hex edges on the plug might start to round off. Sprayed with some **** I had lying around and came back an hour later. Still not moving with a 3/8 ratchet and 8mm hex bit. Out with 2 feet of pipe over the ratchet and eventually the plug came loose.
Looks like the filler plug had thread lock on it (the same as the filler plug) and it must have been fitted by a 7', 20 stone Italian muppet - the manual says 1Nm for the filler plug (no thread lock) and 5Nm for the drain plug plus thread lock.
Poured some old oil back in through the filler hole just to make sure it was the correct hole and oh bliss, it came out of the drain. So that's the right hole then. Lock thread back on the drain plug, 3lt of oil added, filler plug back in (with thread lock - yes, I know, I could have omitted the thread lock but I forgot and got carried away lol), air box back in, plastic on and job done.
Thank god I won't be doing this again for a long, long time but heh, it'll be a piece of **** next time.