Nice images! I also struggle with elongated stars with the MPCC.
I think you should first rule out the source of the tilting.
Go to a star rich area with a bright star in the centre. (For example Deneb)
Make sure to tighten the screws while pressing the cam against the focuser.
Now use the bright star and a Bahtinov mask to achieve perfect focus. Take an image .
Now rotate the camera by 180° and make sure to focus again. Take an image.
Now compare those images (with same orientation, to avoid confusion)
Case A : The same stars are stretched -> The tilting happens inside your telescope (Either focuser, secondary mirror or primary mirror).
This probably means you have to "just" collimate your scope. (I say probably because it could still be tilt due to a poor attachment between focuser and CC and its just coincidence, that you get this result. To be sure, just rotate again by 180° and see if still the same stars are misshapen.)
Assuming your 2nd mirror is descently collimated, you could first try to adjust the primary mirror while still having the bright star in the centre of your image in live view. Turn the screws so that the stars wanders in the direction, where you have more elongated stars.
Then focus again and take a picture. Repeat those steps until the elongated stars are similar on all corners (or perfect in all corners ).
Now you can worry about perfect spacing. Try with different spacing rings on a similar target with a bright star in the middle many stars around.
I cant stress enough how important it is, to refocus everytime you touch your focuser. Otherwise it will mess up with your findings (Speaking from experience..)
Case B : The elongated stars are now in the opposite side -> This means the tilting happens at the CC or in the camera.
This could mean its due to poor attachment.
If you still get the elongated stars on the opposite site, no matter how carefully you attach it, the tilting is inside of your CC, inside of your camera or at the attachment between camera and CC.
First thing i would do now is to lend a DSLR from someone and see how the CC works there.
Case C : Stars are now somewhere completely else elongated -> tilting is probably caused by poor attachment. (Those two screws are not very reliable as @alacant already pointed out.)
If you still have assymmetrical elongated stars after you ruled that out, you could now test if its Case A or B
I hope this helps.
Good luck and CS, Patrick
PS: i know in my pictures above its not perfect, but its good enough for me to dont care.
Altough, right after if went through this procedure (Mix of Case A and C) i got the following result