We have run 250 Verado's now for 5 years, they are cracking engines.
We had the "standard" gearbox's on them for the first 3 years and found that every 360days (I kid you not), the counter-rotating gearbox ate itself. This was, in year one replaced under warrantee, and in year 2 as a goodwill gesture.
In year 3, when it failed again (remember the other gearbox was still original and in first class condition) our service agent had discussions with Barrus. In a fabulous act of customer service, Barrus replaced both gearbox's for the larger heavy duty box's.
Since then, they have both operated flawlessly. I would say the box's are smother and quieter. We had to tweek the prop's to get the rpm right at WOT.
I understand that since 2011/12, Barrus no longer supply the counter-rotating engine with anything less than the heavy duty gearbox.
My advice would be to approach the supplier of the engine and if that fails, talk to Barrus.