+1 on everything that has been said.
- Get trans vent installed asap if not already installed , this will prevent pressure build up in trans/primary.
- oil on top of crankcase under starter is from the starter or starter gasket , usually does not migrate lower , stays on top.
- do you have a airbox drain bottle ? or a plugged or open drain line ?
- check tightness of screws and leaks from sump plate , primary cover , countershaft sprocket area , oil migrates over.
- use a trouble light and find the oil trail after your ride and pin point it. Clean engine before you ride.
- 961 engine will be oil tight with no leaks , find and fix.
- not all starters are leak free in the past. Norton now deliver LEAK-FREE starters. Ebay starters may leak (I know now)
- Buy Genuine Norton Starters they are prepped and sealed now ..
- Rear Shocks , At the bottom of the rear shocks there are lock nuts , these must be slackened and the bottom shock eye turned out (unscrewed) to lengthen. If you want to shorten the shock you may be out of luck because they come from Norton at shortest setting . (Ask me how i Know) . This is all in the service manual which hopefully you have now.