Are you using a tracker at least?
I think my next big upgrade from a basic Star tracker, which does work for stuff like this, is a GoTo mount with tracking. I know there is also software that continuously monitors an image and communicates with the mount to ensure your intended object stays locked in frame (this may be the auto guider you mentioned) - I have not looked into this
1 more question I forgot to ask earlier - what camera body are you photographing with?
When it stops snowing here, I'm looking forward to trying out my new Canon EOS R8, which I think is going to be a decent upgrade from my Rebel T3i (aka Canon 600D)... better low light performance off the bat, full frame which means I can stop doing crop sensor conversions, and higher MP count. Not to mention it's lighter which will stress my tracker a bit less (with a heavy lens I was basically at the weight limit already).
and while you are at it, what 500mm lens are you using?