I downloaded the service diagram and found that Karcher had used at least six different sizes of o-rings (and that didn't include the large gasket seal on the motor). Why so many different sizes? There is 12 x 2mm, 11 x 2mm, 9 x 1.5mm, 6 x 2mm, 4 x 2mm, 3.69 kpl (that's what the parts list says)
Is is usual to have that many different sizes in a pressure washer? Some of them aren't in the o-ring sets available from Screwfix or Hilka.
But it could just be Karcher - the first problem was getting the case off. No posidrive or even hex-headed bolts, of course. Karcher have to use Torx. And not just one size, either. There are three different sized screws, 20, 25, and 30. Why? Couldn't they find a single size which worked?