Oil level problem - help...

Recently my SD has been showing it's oil light at me every time I have to brake hard. Looking at the oil level tube on the left of the bike <gasp> I couldn't see any oil level at all! I checked against a mates SD and his looked fine (was just checking what to look for in the tube, as all my other bikes have a sight-glass window) so I thought I'd better top it up a little. I did this straight after the ride home, so the engine and oil were warm. Up on the paddock stand it went.

I started by adding 0.5l at a time. The manual recommends waiting 20-odd seconds after topping up for the level to reach the tube. Zip. Added more. Nothing. More. More. Then the reservoir on the RHS was full....and still nothing in the sighting tube!! 2l was used from the oil bottle.

I turned the bike over a few times and let it run for all of a few seconds (not wanting to run it with too much oil in!!) and STILL nothing showing in the sight tube. I've now let it settle over-night and still zip.

Any ideas what might be wrong, before I call the dealer??
Also is it simple enough just to undo the small drain bolt and let a little flow out so it's not tooooo over-filled?

The oil tube on my Superduke [07] has always been full right to the top passed the max mark from the day i picked it up new.
Its still showing full after 2000+ miles.
If i put my bike on the rear paddock stand the level drops about 1/2 inch so always check while the bike is level on its wheels.
If you overfill just drain a little out but as its an oil tank and dry sump then overfilling a little should not be a problem.

Maybe the tube has a blockage in it?

Its removable, so if this is the case easy fix... other than that I dont know.

Good luck,
Gary