had bad experience with my CTO 15" rMBP mid 2012, they replaced a screen back in 2013 and the fan back in february this year.
just this month, they approved a screen, flash storage and top case replacement but the service provider here in Manila is having difficulties in ordering the parts because it requires permit from Customs before they can place order on the parts.
they gave me an option to order the parts through another AASP but it requires the other AASP to have the technical log of my Mac, which means i have to send my Mac to Manila again for diagnostic. bare in mind that i'm living 3 hours away from Manila.
I called Apple Care to get an exemption for the technical log and after a few hours they called me to let me know that i'll get a replacement unit rather than the exemption that i was looking for.
The replacement unit that they'll provide is also the one that has the highest spec, was really surprised with their decision
I guess it would make more sense to replace the whole unit rather than those parts, but bare in mind that nearly all parts would have been changed as the top case encloses the trackpad, speakers, battery and they're not removable.