To improve the periodic error in RA here is what I did with an 8" LX200, and my 12" LX200GPS.
Using a high power eypiece centre a star near the zenith and watch its movement.
If you think it needs improvement then loosen the RA clutch and rotate the 'scope to face east. Re-tighten the RA clutch and slew the 'scope back to the same star.
If there is not much improvement then repeat the proceedure until you can see a tracking improvement.
If you do improve tracking significently then never loosen the RA clutch again.
With my 8", I was able to image for 4 minutes unguided. Probably a miracle.
The 12" has improved a lot from its original errors.
Give it a try it may help.
Vince G
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