In my limited experience, the difference between BGN and EXC graded camera bodies at KEH is cosmetic. There should be no difference in function. In any event, given KEH's very liberal return policy, it's a pretty low-risk purchase: I'd say get the BGN graded XA, run a roll of film through it to test it, and if there's a problem return it.
The XA is a terrific little camera, both as a back-up and as a stealth shooter. Nice sharp lens, too.
FS: Zeiss-ZM Planar 50 plus hood, Pentax MX, Voigtlander Ultron 40/2.0 SLII in Pentax K-mount, Takumar 100/2.8 and 35/3.5 lenses: See my ads in Classifieds
M3, M2, R2A, IIIc, IVSB2, & T, and assorted LTM & M lenses
Minolta XD11, Pentax ME Super, and assorted MD Rokkor and Takumar lenses, Rolleicord III, Rolleicord Vb, Rolleiflex Automat MX-EVS