Davo, I'm not sure if it's just the angle/position that you took the pic from, but the top left/right of focuser, spider, looks slightly 'curved' to me. I put a rule against the monitor,(flat), & it lines up with the B/left to T/right, but not with the other 2. Could be just the angle.
I get a similar thing with mine, just out of focus. When in focus it's gone. So I use it as a guide sometimes. Helps to have an electric focuser tho.
HTH.
L.