Hi Alexander, I am using an OAG and have the same drift in RA. In my case it's very slight and only noticeable when zoomed right in. I'm leaning towards PE, as the drift has become less noticeable since I did a belt mod to my mount and tightened the worm drive a bit. Here's a link to a discussion on the subject.
https://stargazerslounge.com/topic/2...r-drift-in-ra/