>I've read various comments that the 12" [LX-200] uses
the same mount [as the 10"] and may be a bit heavy for it
without modifications.
It isn't quite the same mount, but it does appear to be the same bearings, gears, and electrical parts, so where the rubber meets the road, the similarity runs deep. From here on out I'm going to explain why the 12" appears heavy for its mounting and what to do about it, so those with no interest can stop here. Those with an interest should take heed - this advice is developed after a *lot* of real-world experience with these scopes!
The main difference between the two telescopes is that the 12" is much more severely out of balance than the 10" as it comes from the factory. In addition, it is impossible to bring this scope to balance by adding weight to the center of the instrument back; i.e., getting just the right weight of CCD camera or other instrument will *not* work. I said earlier that out of balance mountings were an indication of how much was known about mount engineering; draw your conclusions accordingly.
It has been my experience that LX-200's are not robust to out of balance conditions. Every time I've seen an operational failure, I've seen the user has been using it without anything close to a properly balanced condition. Making the motors work consistently at high torque seems to blow something up in the Meade electronics. This should't be so, but is; forewarned is forearmed. A simple demonstration of the effects of out-of-balance can be had by putting an ammeter on the DC input; an out of balance scope will often show 2 or 3 amps drawn while slewing (even though the Meade "ammeter" on the front might show just an amp or so at the same time).
On the other hand when the 12" is balanced it might peg 0.6 amps while slewing. To balance my 12" scope, I had to add close to 25 pounds of weight. The weight had to go on the top front of the tube, the bottom middle of the tube, and the top back of the tube, with the top-tube weights offset a little bit L-R. I also had weights put on the inside of the east fork, and also outboard of both forks on the 'downward' side. I'll try to dig up my wife's digital camera and put some shots of my balancing system on my website sometime today so you can see what I'm talking about - it might be hard to visualize.
Just throwing a couple weights on the OTA to counter balance the camera/filters/focuser is *not* enough! A lot of vendors offer balance accessories that help you do that simple counterbalancing. They are a good start but are not adequate. You *must* balance for every sky position. In the case of the 12", this means balancing the tube in roll, pitch, *and* yaw - it is out of balance in all of those axes. (The tube COG does not lie on the center line of the OTA - it is an inch and a half away from the optical axis toward the west, and far forward, when mounted on the fork with no instruments.) I have very rarely seen anyone go to the trouble of balancing even the OTA in all these separate axes, but once that is done, you are still only halfway there.
Then, you must balance the fork arms both E-W and front-back. The center of gravity of the fork arms is several inches toward the meridian/in front of the telescope and also several inches in the direction of the Dec motor. That has to be brought back to a position that intersects the RA axis, or else the slew motors are basically lifting weights when looking anywhere other than at the zenith. And lifting weights is not what you want to do.
Once you have a balanced situation, you can of course add some axis preloads which will improve the slewing and tracking substantially. But there is no point having a variable and shifting preload, which is what you get by leaving some element of the scope or fork out of balance.
WRT balancing fork-mounted SCT's, the true master in this arena is surely Dean Koenig at Starizona on Oracle Road in Tucson. Anyone who asks me to balance their scope is quickly going to learn that Dean is my subcontractor for this. I had him balance my scope, and he did it a lot faster and better than I could have, so consider this a recommendation.
In the "gratuitous statistics" department, I used a script called "burn in" to slew my scope several thousand times before deploying it (trying to force it to fail). Since then, I've conducted 27,536 slew operations with this telescope while observing. I've got no discernable wear on either the RA or Dec gears, I've never blown a fuse, and the scope shows no sign of failing anytime soon. The main wear and tear is owl poop and having the scope rained on once. By contrast the out of balance scopes I've serviced develop noticeable wear on the gears in just a few nights and often lack factory fuses according to their owners.
One more item - these scopes last much longer if you don't slew them at warp nine. Set the slew rate down to the slowest slew rate the telescope supports. You will be rewarded by considerably less gear wear, at the very least. At most, you will find the motors aren't chewing up the gearing in the reduction boxes and contributing to new sources of periodic error, as well as possibly creating burrs that the drive system can get hung up on long enough to damage the telescope.
Oh, one more item again - strip off the chinese mystery grease that Meade uses and replace it with something else. I have a recommendation, but I'll have to look it up; I'll post back on this.
Obviously, all this advice goes equally well for any size Meade, or, I suspect, almost any telescope at all.