Cool. Please let us know if you're somehow able to get ahold of one of these.  I'd like to buy a backup given all the issues we've had here.  These things are very simple to replace, just a few screws and connectors.  I was hoping maybe the vendor had a quality issue with a limited date code range, but given the others who have had blown transformers on newly purchased amps, I'm thinking we're all at risk, even those of us who have had theirs replaced recently.

Also I'm curious if anyone has approached Mercury for a higher quality replacement?

Finally, having some background in electronics and repair, I'm thinking the cause of these transformers going out has nothing to do with amp design, using attenuators, switching topologies, etc.  I think these things fail because the windings are not properly coated at the factory, leading to breakdown of the insulation over time due to heat.  When mine failed, it took out a breaker in the house.  The primary side was completely shorted.

If Line 6 were serious about resolving this issue, they'd be getting these failed transformers back to the vendor for failure analysis.  Also, they'd be working with an alternate vendor to use while this vendor gets their process in order.  I suspect that neither has happened, but then again I wouldn't have access to information to prove otherwise.