if the secondary is a bit bent, it would also produce astigmatism on axis - have you seen any? If it is only off axis, would look more closely at the CC than the Newtonian itself.
Slight complicating problem is that astigmatism can come from the primary mounting, the primary mirror figure, the secondary mounting, the secondary figure, the CC fabrication quality and the CC spacing - but I guess that isn't helpful
Agree though, secondary mounting is a big issue.