I got the scope out again last night but conditions were still ordinary with jetstream overhead. Looking closely I saw some astigmatism close to focus, then I put another scope on the mount and saw exactly the same pattern so I guess it's time to visit the optometrist again
Trapezium E was solidly visible at 100x with F coming in and out.
Note: I have to correct an earlier comment about the focuser not properly holding the diagonal; I used a Televue diagonal the first night and the safety undercut obviously doesn't mate well with the 127's compression ring since a William Optics bevelled diagonal nosepiece is held securely. The Hioptic supplied diagonal has the bevel as per WO and it appears to be of decent quality compared to a WO diagonal. The focuser is still not great but it is servicable for visual use.