The problem with the slipping clutch has been solved in the meanwhile. I ordered new springs and one new friction discs as one got stripped of before when installing a new set of friction discs and steel discs. Due to the broken circlip. When I arrived in Lima there where no new springs, but there was another DR650 in storage at the Suzuki dealer. The owner allowed me to take his as I payed for new ones for his DR. If you look at the picture below you can see a big difference in the old ones (left) and the ones from the other DR. I reckon that the 'new' ones aren't stock as the diameter of the spring thread is thicker and is over 40mm in length.
I've replaced the inner basket and clutch cab as well as these were worn out. 700km off-road later the clutch works perfectly