I have a Mid-2012 rMBP. The first logic board had sudden GPU panics and crashes until the board eventually stopped powering on. Since it stopped powering on, Apple refused to replace it. At great personal expense I have imported two different logic boards to Canada and performed the replacement. The exact same crashes persist. So I am starting to think that this may be not a Logic board issue - and I am looking for help tracking down the problem. Thank you.