I can't remember seeing out of memory errors caused by a hardware problem (doesn't mean it's not possible).
And unfortunately, Mac geniuses are often not geniuses, (but that doesn't mean they're always wrong).
I understand your frustration, but let's try an eliminate other possibilities.
out of memory errors when rendering are usually caused by using cmyk or grayscale graphics or a non fcp friendly format like h264 or mp4. And the problems can be intermittent so although you may see the problems on one machine, they may not turn up immediately on another system.
What are your sources and what are your sequence settings?
If you want to send me an xml export of your sequence, I'll take a look and see if I can figure out what the problem is.
Solution to it all ended up being:
using After Effects, then pushing out same files w same suffixes. laptop now can see them....after a full day lost of trying to get it to work.
Don't buy a retina laptop folks. The superfast thunderbolt isn't friendly and the enclosed model is quirky at best..no, I take that back...crap is crap.