Be sure those thin parts are oriented parallel to the direction of motion of the wiper/mixer. See my photo above (Sep 20) with the ✘ and ✓ icons.
Have you tried angling it some more? At least enough to eliminate the internal supports and turn them into regular ones.
What layer height and printer are you using?
EDIT: I had a quick look at your STL and noticed in the position and orientation you illustrated above there’s likely cupping. You might try an orientation like this instead:
I’ve rotated the part so that it’s in line with the wiper motion (i.e. perpendicular to the wiper itself). I’ve also placed it on supports (using density 1.35) to eliminate the cupping, and tilted it. Then I added a few more manual supports near the start of the print. (If you want to print direct-on-base, which is otherwise fine for your geometry, then you’d need to add a vent hole to your part).
Here’s the file if you want a go:
rumpf_often1.0-27.12.20-edited.form (498.0 KB)
Others may have more time to examine this and improve or refine what I’ve proposed.