The leaf spotting resembles a fungal disease called Cercospora, which can be common on Rhododendron foliage. Old tissue that has died can bleach in color and develop this grayish tone, though similar bleaching/drying can occur with simple sunburn, either with too much exposure to direct afternoon sun or in prolonged dry spells. Fungicides are not going to cure Cercospora or any other leaf spot, so management focuses on sanitation (remove fallen leaves the plant has shed) and keeping plants otherwise minimally stressed; ideal conditions are the same as for their azalea kin. You can snip off and dispose of any of the most unsightly leaves if you wish, but the plant may shed them on its own in time as new growth replaces them; otherwise, if left alone the rest of the healthy leaf tissue in a damaged leaf is still supporting the plant with photosynthesis.

Isolated branch death could be due to one of two different pathogens - Botryosphaeria or Phytophtora; the former infects branches on drought-stressed plants, and the latter can either infect stems or roots when drainage is poor or wetness prolonged. No chemical intervention will impact either after the fact, but trimming-out dead stems as they appear and monitoring the root zone for moisture levels is all you can do. If a sprinkler system is used in the yard and wets the Rhododendron's foliage, be sure to run it only when needed and only in the morning hours so the foliage can dry by nightfall. (Or perhaps an overhanging roof gutter occasionally overflows and drips onto the plant?)

The cause of the flower bud death may vary from environmental issues (like late frosts after they've broken dormancy and begun to swell - this happened last year - or wet years promoting Botrytis rot of the bud) or root stress, as flower buds tend to be aborted by a plant under stress before it begins shedding leaves or manifesting other damage. There's not much you can do except to keep the buds dry (with regards to any intentional irrigation).

The repeated appearance of new growth in years past is encouraging, as it suggests that root health probably isn't too impacted, since functioning roots are needed to support new stem growth. So far, this year's flower buds appear to still be viable, so hopefully they will open normally.

https://extension.umd.edu/resource/azaleas-and-rhododendrons-common-diseases-and-abiotic-problems

Miri