I was recently shopping for a cutter. I ran across some posts talking about driveline problems with that cutter. I didn't see that often enough to be concerned about it. I can't answer your question about a manufacturer fix in later models.
I ended up buying a JD1008 cutter. It's considerably older than the MX models. A dual spindle cutter has one issue that can cause catastrophic failure if it's not monitored. the blades are timed because they overlap in the center. If out of time, they will hit each other in the middle and more than likely cause gearbox shaft failure. All dual spindle cutters have a driveline assembly that keeps them in time. Some manufacturers have had problems with that system failing and letting the blades hit. Don't want to get into a brand war so won't mention what I found to be the worst at having this happen, but it wasn't the MX models.
I bought a fully mounted cutter because I do a lot of cutting in woods and deadend waterways where I need to totally pick the cutter up and/or back into an area to cut. I would estimate the MX8 to weigh around 1500lbs. You may need front weights if you carry it. I had to add 650lbs of front suitcase weights on my 7500lb tractor to carry my 2000lb cutter.
If you are cutting in open areas I agree with Jim, I'd go for semi-mount. That design requires a rear remote to run the hydraulics on the rear wheels.
An ideal situation to me would be fully mounted with hydraulic operated rear wheels. Gives you the ability to change cutting height on the move.
