I've had nothing but success working with Mesa Customer Service.
I had about a month turnaround from the day it left my house til the day I got it back with my Mark V 90. I had the well documented diodes issue on my 2009.
They also tested two full sets of tubes I sent. EL34 and 6L6's.
The only issue I had is that the bell housing on my main transformer has a pretty good dent in it that it didn't have previously.
I'm not sure how that would happen, or if I really want to know. But I made sure they documented it in case it becomes an issue somehow.
Anyway....
The fix was relatively inexpensive. $140.00 with return shipping. And now, it absolutely sounds better than any other time I've owned it since I purchased it 2016/2017. It would be nice if the repair technicians would take notes about the repair and the exact work they've done, and send that information back to the customer.