I have a 2008 KTM 450 EXC which has been recently re-built. This included Full main bearings, shaft seals piston rings cam chain ect ect. Since then I have has a contant issue with oil migrating from Engine to gear box. Normally takes around 2 hours running before starting then goes over quite quickly. We have replaced all seals and the main seal has been done 3 times. Using Motorex oil. Checked engine venting OK. Has anyone else ever had this issueor any suggestions of how to fix?