I know some folks that bought a new valve and installed then took the old one, took apart and soak in hot water and clear vinegar solution. When the new one get hocked up with barnacles they just switch it out. Those valves used to be big bucks but now they are cheaper. Just FYI.....some of the Excel floor plans requires you remove the WH to service the mixing valve. I know cause I watched Vaughn (Pete) switch one out on his demo one winter in the RGV of TX. I loaned him some tools to do it. Thankfully most can be done without R&Ring the WH.
We've been lucky and on our 3 Excels that had this system, we've never had a lick of trouble. I believe flushing the HW tank regularly and only using soft water helps.
I know Watts has an adjustable valve that's real cheap.......but I personally don't know anyone that's used it. This subject has been discussed here in the past. There's two different temperature levels. Personally I think I'd use the higher temp one