The pictures are too far away to see the white spots but it could be pestalotia leaf spot, a common fungal infection best treated by making sure the environment is not too humid and by applying good sanitation techniques such as watering only the soil (no overhead watering) and watering early in the mornings, cleaning up plant debris in the soil and disposing it in the trash (do this to the leaves when they fall in the Fall), replace the mulch with new mulch if the infestation is spread thru a large percentage of the leaves, allow for more separation between plants in order to improve air flow, etc.

Luis

I could not access the photos, but let me suggest that nearly all deciduous azaleas/rhododendrons will have various leaf spot ailments, mildew, etc. at this time of year. These are generally more unsightly than a threat to the plant's overall health. Cleaning up the leaves once they've fallen as luis pr suggests may help for next year, but it's likely that the leaves will exhibit the same discolorations next year by late August/September.

'Gibraltar', btw, is one of the many Exbury, not Duxbury azaleas.