I am going to diagnose wind and weather damage rather than a disease. The older leaves look in worse shape and I suspect the plant could have dried out in the summer making these older leaves more susceptible to wind or sun damage. If you send me a close up of the leaf damage perhaps I could make a more accurate diagnosis. I suggest you add a wood chip mulch on top of the roots of the rhodies but do not let the wood chips touch the trunk of the shrubs. Make sure the rhododendrons are not planted too deep as they have very shallow roots. Looks like the rhodie in the photo is planted on a slight slope. This could be making the water runoff so it suffers in dry times. Put a slow leaking hose near the roots during droughts to really soak the root ball once a week. Remove any unsightly leaves and after the plant blooms (I see flower buds) you can prune off any long, bare branches to shorten them up. New leaves will sprout just below the pruning scar.  Keep growing, Marianne Binetti