Employing the Argonne Fragment Mass Analyzer and the implantation-decay-decay correlation technique, a weak 0.50(21)% proton decay branch was identified in 108 I for the first time. The 108 I proton-decay width is consistent with a hindered l=2 emission, suggesting a d [Formula presented] origin. Using the extracted 108 I proton-decay Q value of 597(13) keV, and the Q α values of the 108 I and 107 Te isotopes, a proton-decay Q value of 510(20) keV for 104 Sb was deduced. Similarly to the 112,113 Cs proton-emitter pair, the Q p (I108) value is lower than that for the less-exotic neighbor 109 I, possibly due to enhanced proton-neutron interactions in N≈Z nuclei. In contrast, the present Q p (Sb104) is higher than that of 105 Sb, suggesting a weaker interaction energy. For the present Q p (Sb104) value, network calculations with the one-zone X-ray burst model Mazzocchi et al. (2007) [18] predict no significant branching into the Sn-Sb-Te cycle at 103 Sn.