I have 10 MC012 preamp bodies at last count: 4 originally from The Sound Room, and 6 originally from GC. Of the 6 from GC, two have had problems due to dirty PCBs (LF rumble noise)- easily fixed by defluxing the board. One was profoundly dead out of the box (I bought several of them in a panic, without listening to them, while on the way to a live gig for which I needed more mics). The dead one I replaced with a refurbished unit from The Sound Room. The ones sourced directly from The Sound Room have been no problem at all.
Ditto on the capsules that came from there: no problem. Out of the 25 or so capsules I have, the GC capsules have only turned up with one problem, and that one was really cosmetic: the screen holder on one of the cardioid capsules was loose and would fall off (shipping damage, about which more below). Some superglue fixed that. I've had no problem at all with diaphragm tension, or contamination causing leakage or noise. None of my capsules qualifay as a dud.
The most telling thing to me is the condition of the mics when you first get them. The GC mics are packed in those little plastic clamshell factory cases, with the capsules in pockets beside the preamp body. Look at the bodies for little fingernail-shaped dents: those are caused by the capsules bashing into the preamp body when the box is dropped (or maybe the whole pallet of boxes!). *Every one* of my GC mics has had at least one such ding when the box was opened when new. Only one of the Sound Room bodies had that, and it was the one that I bought as a refurb... Maybe that speaks more to abuse suffered at my local GC, and less to Oktava's QC. Your mileage may vary: but mine from GC had consistently taken a bit of a beating, and the dents tell the tale.
Moral of the story: if you're going to take these mics out for location work, make a better road case for them. The factory clamshells are completely _useless_...
The mics themselves, on the other hand, are definitely _not_ useless. They are the best bang-for-the-buck going in SDCs, for my money, and are very applicable to a lot of situations. Dents and all! Put in a little TLC, and you'll find them to be good mics that will serve you well.