Ok ive pulled the gearbox out of my new 84 k100 as i wanted to go through everything to make sure its all ok. there was some oil sitting under the clutch plate so im assuming thats either from the box or the engine leaking through the rear main. there also seems to be a bit of a leak out of the final drive as well. so question is how much is suggested while i have all this out and where is the best place to get the parts.

If you have the gearbox out put a new rear main seal in, it probably has never been changed.
I use a viton seal that is 8 x 50 x 80mm they will sting you for about $80 but scream like a stuck pig and say you got one for the other bike here last year for $34 and they probably will relent. If not go elsewhere and try it.
smell the oil to tell where it came from, gearbox oil has a very sulphur smell.
Final drive seal is very easy and straight forward. If the disc bolts, 2 socket head counter sunk, are difficult use heat to soften the loctite. Remove the 8 x 8mm socket screws and split the case and replace the seal taking care to make sure the running surface for the lip is good and clean. Replace the seal and making sure the O-ring and shims are in place.
Parts I usually buy from Motobins in UK but seals are available in Oz. https://www.motobins.co.uk/

Thanks Rick, where can I get the Viton seal in tasmania/australia should I replace the seal in the front of the box as well or is this tricky ? I'm assuming the oil is rear main as more oil has appeared since the box being out

Any of the big bearing suppliers will have them or be able to get them I buy most of mine at State wide Bearings http://www.statewidebearings.com.au/