I have the 12" and I have routinely run the scope with hugely imbalanced loads without issue when everything was right with the scope, with the emphasis on the "everything is right" part. I have used everything from image intensified eyepiece to Binotron B27 with Nasser zooms and when everything was right, never had any problems caused by imbalance.
If everything is not right, you can have problems.
Here are the things to check.
Check that all base hand knobs are tight. If you have not done this in a while, I will tell you that they can loosen.
If the altitude clutch is tight but the scope still moves up and down some (you feel some play) remove the truss assembly from the base and check to see that the screws that hold the dovetail saddle plate (the casting that the dovetail on the scope slides into) are all tight. If they are not, you may want to pull them out and put some non hardening Loctite on the screws before putting them back in, and when you put them in, get them tight.
Next, while you have the scope out, look at the bearings on the opposite side from the dovetail saddle casting; the bearings that support the non drive side of the scope. These bearings may have rubber tires on them. These tires were originally glued to the bearings. If the glue has failed, these tires will deform under the pressure of the scopes weight and walk or squirm on the bearings. If you detect that they are loose, my advice is to just rip them off and let the bearing races run directly on the plastic drum.
Now your scope may be different than mine in design but in the pictures the design looks similar.
Next is backlash. Unless something has changed, the manual gave about zip with respect on how to adjust backlash.
Before I type this instruction for about the fifth time on CN, let me apologize in advance for typo errors. I am traveling in NZ and the letters on my keyboard is upside down and th horrible virtual keyboard is painful to type on. Also, since I am not at my scope, I have to go from memory. This means I might get something reversed, but some trial and error on your part should sort it out.
First, go to a star low and south (as close to south as possible but it does not have to be exactly south). This star will be used for the as backlash adjustment. I forget but I think it is Utilities/backlash/azimuth. You might have to look around for it. As I recall, when you find it, it should give a value.
What you are going to do is to use your reticle eyepiece and center a star in the field. Set your slew speed to 3. Now, using the Right button on the controller to move the star away from the center of the field maybe half way to the field stop. Next, watch carefully... Using the Left button, bring the star back to the exact center of the field and exactly as the star hits center, let go of the button. If you overshoot, start over. Once you let go, wAtch the star. If the backlash is set properly, the star should stay exactly centered. If the star appears to drift a little before it starts moving, you need to increase the backlash value. If you see the star appear to bounce back in the direction it came from, you need to decrease the value (I believe the value is arc seconds?) increase or decrease as necessary so that when you release the button, the star stays centered and does not drift or bounce back in the direction it came from. When you have this right, exit the AZ backlash routine.
For Alt, you will use a star low in the west. Does not have to be exactly west. The process will be very similar, but this time you will center the star, use the Down button to move the star away from center, then the Up button to bring it back, and once again, work until you have a value that keeps the star centered.
What you are doing in both cases is driving the scope into position against the direction of movement and seeing if the motor driver takes up the proper amount of slack to get the star moving again as soon as you let go of the button. If the star bounces back in the direction it came from, the motor driver is turning too far in the driving direction.
The reason I use the south and west stars is just to isolate the different axes as much as possible.
Now again, I can't be sure that the mechanical are the same and it is possible that the controller routines have changed since I last did mine.
Record the values (I just wrote mine on a little scrap of paper and clear taped it to the controller). If you reset the controller for any reason, just reenter the values.
There is more. PAE Values. If you are using the PAE values, be aware that these are saved at power off. Now if you always left the scope in exactly the same position then once set, the PAE values would never have to be cleared. If though you are using PAE, and you never ever resetting them, you can accumulated incorrect data. I recommend clearing PAE at the start of each session and rebuilding the PAE data for each session as you go along.
Last.......... If you are manually skewing, be sure to sync your encoders frequently. Procedure in the manual for this.
Ok, I am not saying any of these things are your problem or that any of these things will fix your problem. What I am saying is that if all of these things are right on my scope are right, my pointing is good regardless of my imbalance with any load I use, and there is a huge range of Payload on my scope. My scope just does not care about imbalance in the slightest and when all of these things are right, my go2 performance is pretty good (though there is always gimbal error near zenith, but this seems to be a general characteristic of alt as go2 mounts.)
Darn that was hard to type on a virtual! Keyboard. I hope something here was valuable to to you and I hope I have the button directions right.
Good luck with this. I probably will not come back to this thread but I would appreciate a PM if this helped, if you have corrections, new data, or found some other problem.