Thanks Phillip,
Comforting to hear that other SCT's seem to have the same behavior.
I would agree with you if I could replicate the behavior at all points on the focuser travel. There are two points of contact where that reasoning holds true, the barrel that the lead screw turns through and the joint at the mirror carriage. If the joint or barrel was the weak point, the behavior would be observed at all points of focus.
I'm going to have a go at trying to test multiple points in a 10 turn range around the prime focus point. Need to fabricate a spacer to extend the EP out another 10mm or so. Not sure yet how I will go about shortening the focal plane, but I may not need to. We'll see what the results are of my first test.
Just have to wait out this weather front passing through
.