Thanks guys,
latest is; I took the seal to the local gearbox repair specialist, he said it looked like new and was unlikely to leak unless the drive hub was worn (it isnt). He also said that he had seen sealant used in the centre of the roll pins and since the roll pin was broken that was the more likely source of the leak.
Which brings me to the more important issue, of why the roll pin broke. I note that it is actually broken in 3 pieces, the third one had fallen out already. The pin has broken at both interfaces of the shaft / drive hub.
On reassembly, I noted that on full droop, the holes in the shaft and hub are about 3mm out of line. So with the pin in, the suspension droop is limited by the drive shaft, and the roll pin carries the full force.
Clearly I need to fix this, the easiest option is to turn the rose joints out another 4mm I will still have enough thread engagement.
So the lesson here is to make sure that there is freedom of movement in the drive shaft over the full suspension travel.
regards
Dave