Thanks Uncle Rod, the serial number reads horizontally from left to right looking at the corrector (as if to look down the ota) with the dovetail on the left - the ota is orange from a Nexstar 6SE. The secondary holder stops at that point and won't rotate further clockwise, but will loosen up if turned the other way.
I did receive a response from Celestron support which confused me as much as anything else. The serial number may or may not be present, depending on model, etc. They suggested removing the secondary and the corrector plate and looking for the aligning marks to put it all back together correctly. If I could figure out how to actually get the secondary out that'd be a bonus
