Long distance diagnosis is never terribly reliable, so I'd suggest you take a leaf and/or the picture to a local nursery that sells lots of rhododendrons - one shouldn't be hard to find in the prime rhododendron area of BC. In the meantime... The areas that look white are necrotic (dead) tissue. The brown areas will likely turn white after a time. The most common cause by far for this is exposure to winter cold, wind and sun. It's the result of mechanical damage rather than disease. The browning you experienced over the summer may have been a result of too little water. Same effect - dessicated tissue - but a somewhat different cause.