Brian, I'm not sure. I've had similar things happen when moving standards from one Cambo rail to another or to an 80/20 brand 1" square t-slotted aluminum extrusion. I fiddle and eventually things come right. I also help the standard I'm trying to move go. I generally don't clean rails, but you might try that.

About the 1"x1" t-slotted extrusions, they're the least expensive long rails for square rail Cambos. My 48 incher cost less than $20 delivered.

By the way, I made one misstatement earlier. If the little set screw under the rail rider isn't screwed as far in as it will go (after the standard is on the rail), the standard can rock back and forth a little, giving small unintended tilts. The set screw may have to be backed off to get the standard on the rail.