I had a related problem on my '12 Lacrosse 301RLS. The dump valve handles are under the wardrobe slideout so they're quite difficult to reach. I was trying to close the Black water valve but must have been pushing a bit off-centre and as it closed the handle broke off at the threaded ended. I wasn't able to open it again until the dealer replaced the handle, so spares are available.
I just noticed a week or two back, that the gray water handle was almost completely unscrewed and ready to fall off. It's now held on with LockTite
Recently, while the trailer was in at Lazydays in Tucson, the Service Tech added two metal straps which "guided" the rods to prevent them being pushed off centre and breaking.