Main Motorcycle: 2012 800 Tiger
Join Date: Apr 2007
Location: Rangiora, New Zealand
Other Motorcycle: 1977 T140
If there are no visible leaks around the engine casings then, it is either worn (oil) rings or valve guide seals. Given that, either one is expensive to fix. I would not expect a 2007 with 25,000k to show signs of such oil usage as yours.
Remember this! The French lost, Fuchs oil is French! Revenge is a dish best served cold (and long remembered) try a Pommie oil of the correct grade.