I've talked to Pyramid. They appear to be very knowledgeable and professional and willing to answer questions in detail. So I appreciate that.
The bad news is there is no free, or even affordable, lunch with these ML-23s. They told me the minimum amount I might get lucky enough to spend on the repair is about $2k and it goes up from there.
I certainly believe them, but it does open up the question of whether to do it. I mean, I bought the amp for about $1400 and while I have seen asking prices as high as about $2500, it is an open question as to whether that is the best way to spend $2000. While I have no plans to sell the amp, I also wonder if I couldn't get something better for that same amount. Or just stick with my other amps until I'm looking for a place to flush some cash...