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It's a tough one. At F4 as tolerances are very small. I think it's only a matter of a 20-50um error to show up as poor stars/collimation. You really can’t do this without a collimator like the Cat’s Eye. When you do this sorted, you can move the scope around to different parts of the sky to check if that affects collimation. If it does, the problem could be the mirrors, spider, or it could even be the collimation tool jiggling in the focuser (a problem I have seen with some laser collimators). If using a laser collimator that might even be the problem as the laser is not correctly collimated!
Once you get that sorted you can then fight with camera-CC spacing/tilt. You really need some sort of aberration inspector for this. I’ve used NINA Hocus Focus – it will tell you how much you have to change the spacing & the tilt. You can then point at different parts of the sky to again check if things are moving around.
I've managed to get my skywatcher F4 carbon fibre to generally behave itself, and stay good for a few months. But it took some time to sort out the wobbles (better focuser, spider not tightly screwed, crappy CC wobbling in focuser), then finally correct CC-camera spacing and tilt with Hocus Focus.
I feel your pain, F4 ain’t easy on a Newt. It needs persistence and a few $$ thrown at it. Took me a few solid months to sort it out, plus a break of just using my refractor for a year. Otherwise, F5 is much easier. I remember a thread by codemonkey on IIS a few years ago that went for months fighting with a similar issue.
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