MZ/MuZ Riders

I finally tracked down a persistent oil leak on my Rotax 500 engine on my Saxon Country 500. It's coming from behind the chain sprocket on the engine. It's a pretty good leak and needs to be fixed. Do i maybe just need to tighten the sprocket nut? Is there any trick to this and does anyone know the torque spec for that nut? Or maybe do i need install a new seal behind the spocket where the shaft goes into the engine? Any suggestions appreciated...thanx

seal behind sprocket part number 230-395 atk or ron wood or a good bearing shop 25x40x7
dave
part number and size same in atk book and mz book

Thanks, i ordered the seal from Ron Wood site.....hopefully i don't need a new bearing or anything. The guy at the shop says you can change the seal without draining the oil by laying the bike on its side....