After noticing a small oil leak coming from the drive sprocket area i isolated it to a leaky output shaft seal (part#PFKL1215354). I ordered a new one from Lings here in the UK and went about making a right mess fitting it by trying to tap it in with a hammer and drift, as the seal is a very tight fit.
So, two more seals were ordered this time (in case i damaged another one!) this time i engaged my brain and used the following method to fit the seal with no problems -
-Lightly smear oil around the outside edge of the seal.
-Slide the seal over the output shaft and LIGHTLY press it in about 1-2mm using your fingers making sure it is absolutely in even all the way round.
-Now the clever bit, take the old seal and the spare one and slide them both onto the output shaft flat side first.
-Next take your sprocket and slide it onto the spline on top of all 3 seals.
-Take the locknut and turn it onto the sprocket and SLOWLY start to tighten the whole lot up. If all is going well you should be able to see the new seal slide into place as you tighten the locknut.
-When the new seal is flush remove the locknut and the 2 seals that were acting as a press and bingo a perfectly fitted new seal!!!
Hope that this is of some use to people even if it might appear obvious to the more experienced mechanics out there.
I searched for ages on tips on fitting driveshaft seals and information was a bit thin so i thought i'd share this method