brought my 850 Eldorado home nearing home it started sliding on slight leaning stopped and found oil all over nearside rear wheel tyre took of the wheel expecting oil everywhere but there was no oil ! checked rear axle level and it was fine it must be gear box oil somehow anybody had this before ?
is it engine oil or gearbox/rear drive oil - they smell/taste different 
maybe its blowing out of the engine breather , may get on the back wheel depending on how its routed…(seem to think mine exited on the nearside under the footpeg)
… and I understand that the level plug on the later drive boxes is at the incorrect level (at least on some of them) and just checking it by the level plug may give a false sense of security (and oil level!)… hopefully someone will be along to confirm that, its been a while since i had a ‘loop’
editL: here you go, i knew i hadnt imagined it!
Rear drive level plug - Loop frames - Moto Guzzi - Topics - Gregory Bender
Yes, level plug is too low on some bevel drives with the 6 bolt sump. I have the dimensions somewhere but should always fill by volume which is 360cc. Another issue is oil transfer from bevel drive up to gearbox. Hard to believe but it happened to me but resulted in oil dripping from the UJ area. Can you see where it’s coming from? Filler spits a bit out on mine but if you crack it open when hot it sorts that out.
Thank you for that, I’m pretty sure it’s gear box oil as it smells like cat wee , also rear bevel box was at the correct level. It appears to be coming out of the left hand end of the rear wheel spindle, is it possible for the gear box oil to come down the UJ tunnel along the spindle and out?
Hello again, the oil appears to be coming out of the left hand side of the rear wheel spindle, is it possible for the oil to run down the UJ tunnel, along the wheel spindle and out of the left hand side. The bevel box level is correct and the oil smells of cat wee which I believe to be gear box oil?
yes that’ll be gear oil 
i cant think how it would get there… where is your gearbox breather pipe positionned ?
The gearbox and the bevel box have the same oil in. There’s plenty of oil inside the back end of the swingarm when the bike is moving - it gets thrown forward through the pinion bearing to lubricate them and them runs back through some small slots, but should stay inside.
How do you know the bevel box level is correct? If you have one with a wrongly-positioned level plug it can be down on oil but still run out of the plug when removed. In any case a small amount of hot oil can make a big mess - maybe only a few cc’s have leaked which wouldn’t necessarily change the level enough to notice.
I’m guessing the small inner seal has failed on the bevel box - in the diagram in my workshop manual it looks like there might be a path for oil to get onto the spindle, although I’ve never had it happen. Full stripdown to do that I’m afraid.
Agreed. Come to think of it, it would be much more convenient for all loop owners to live in same part of country…and within easy reach of professional expertise such as Nigel B!
i thought the bevel box always has heavey gear oil in it while the gearbox has thinner gearbox oil
always used EP90 both ends of mine (with moly in the bevel box)
Heavier grade oil (80W-140?) specified for small-block bevel boxes from memory, but big-block uses EP90 in both bevel and gearbox. Still smells the same though.
I always use 80/140 in bevel box, usually put same in gearbox but will settle for 80/90. Never used additives.