Got around to doing the seal today. Before trying to get flange off I gave the flange a good spin with engine running while in 5th gear, concluded it wasn't a breather issue or failed silicone in notch. You can see all the oil in area of nut, looks dry by notch. I think job took me around 4 hours. Did it with gearbox fitted, hopefully the pics are self explanatory but used extension bars and wood props to give me the pivot points to apply torque to remove nut, and and to re-fit them later. When I went to pull the seal out I tried it by hand first and a big plastic washer came out, which was a surprise as I hadn't expected it, turns out the seal had delaminated and the sealing part separated from the part that faces gearbox, (photo of the split seal on flange also shown). I used a socket to pre form the new seal, speedo worm drive measured 39mm, sealing surface of flange 41mm, my socket provided 40mm which seemed like a happy middle ground meaning it would clear the drive yet have to stretch itself over the sealing surface to fit. To drive the new seal in I used the flange reversed around, it went home fairly easily, I could have used a large 50mm socket I had but wanted to know if I ever had to fit a seal on the road in some remote location ( an unlikely scenario). I'm going to leave the seal tension back to whatever it gets to and let the silicone in notch harden overnight before filling gearbox and taking it for a spin. Will be a head wrecker if it still leaks, the R100GS I took to India in 1994 had two seals replaced by dealer ( wouldn't surprise me if they were treating it in same way as for monolever, each lasted about 200km and I spent most of my trip filling the gearbox and sporting a rear wheel plastered in gear oil.
