Ok, so I received the warranty part from FatShark the other day and installed it..
First of all, the replacement part they sent was NOT a new video receiver - Rather, it is the interface board the video receiver module plugs in to. (It also has the headphone jack and the receiver module power switch on it.)
Installation was pretty straightforward - It requires a narrow #0 or #1 phillips to remove two screws on the underside of the goggles. Yes, you must open up the goggles to install it. But, the goggles' construction is nicely modular, so opening up the case won't cause mirrors, prisms, or other parts of the optics to go everywhere.
You'll also want a thin flat blade screwdriver as the case is also held together with locking tabs - one inside the nose indent, and three on the forward edge of the case. You'll have to carefully work them with the flatblade to pop the case open. (If there's an easier way to do it, I didn't figure it out.)
Once the case is opened, you can identify the board fairly easily. Just unplug the wire harness, slide the board out of its slots - there's no screws holding the board in place; it is locked in place by two retention grooves and the case itself when closed - plug in the new board, and slide it back in place.
Have not tested it yet, but I'll post up results once i get a chance. I have two Immersion 5.8 600mW transmitters; one worked fine with the old rx board, but the other one had the wavy top issue. I'll try both transmitters and report my results.