The gearbox in our 2388 went thermonuclear the last year that we ran it. It boiled the oil out the dipstick and melted the teeth off the gears that we were using.
While talking to our preferred dealer's service manager, as he put it, he said that the rotor gearbox's have always been a weak point for awhile. He indicated that most would "Just go" eventually.
We installed a rebuilt gearbox that the dealer had in-stock and we were back up and running in about 24 hours. We could have went with a used gearbox, but we decided that we didn't want to possibly need to do all the work changing the gearbox out again.