I think I bought a refurb

Sorry, I missed the part where you contacted the seller. Glad he’ll make good.

But y’know what? I just took my once-new Fuze out of its silicone skin and turned it on in a dark room, and mine leaks light too. Never noticed it before.

It’s more  a quarter-inch slit than the circle in your photo, but obviously you were shooting in low light, so I don’t know if you actually have a circular hole.  The leak in mine is on the right side–that is, to reproduce your photo, the screen would have to be facing down.

Anyway,  it seems that SanDisk is not exactly precise about sealing that seam. This was a new Fuze direct from SanDisk itself, once upon a time.

I’d be curious what other Fuzers see if they check this out.

Anyway, mine has been working great for two years plus. Your “R” is still a mystery, though–unless it’s some subtle difference between the v1 (mine) and the v2 that you may possibly  have. Or…could it stand for “return”? 

I do recommend getting a silicone skin and screen protector, because the Fuze is very susceptible to scratches. It’s up to you if you think your gap is big enough to endanger the inner workings of your Fuze. The only moving parts are the wheel controls and power switch, and obviously you don’t want to be dunking the Fuze in liquid anyway (though some have survived that). 

Clearly SanDisk itself lets them out of the factory imperfectly sealed–so aside from that R, and possibly even with it, yours could still be new. The mystery continues.

Back to your OP, was there any pattern to the files that made the Fuze misbehave?  All from the same album? Do they behave now? If it’s a software glitch, that can usually be diagnosed or fixed.