I've never had any of the problems discussed here, but I must say that I'm rather anal at making sure that everything that should be tight, is.
I had the end rings powder coated matte black, almost immediately after purchase, so I never used the scope "as is " from the factory.
When powder coating an object, you are actually thickening its width with the application of the powder.
Maybe it was this process that eliminated one of the causes of collimation shift.
My 2 cents.
