Hi Chris,
It's the mount. What is the focal length of the telescope on the mount? What camera are you using (to tell us the pixel size)? These will tell you your image scale. That information combined with the amplitude of the periodic error will tell you the expected yield in percent from a series of exposures. I have a spreadsheet for that here:
http://www.faintgalaxy.com/g11tracking.htm
There are three fixes, two cost money, 1) live with your current yield, 2) autoguide 3) fancier mount, and autoguide eventually anyways...
A good AG setup is not cheap (it either cost some real dollars or takes some time to perfect), but a mount that does not need AG is even more expensive, AG is usually the next step
I did some stuff with a EQ4 unguided. From an aligned stack of 10 sec subs you can watch a hot pixel trace out the PE:
http://www.faintgalaxy.com/ngc6720.htm
You could do the same and quantify the size of your adversary.
Good luck,
EB