Leaves show some evidence of what may be lace bug damage. The overall mottled appearance of the leaves looks to be a nutritional deficiency rather than fungal infection. In the bottom photo more than 6 flower buds are visible. They are concentrated on the bottom branch which has grown in this manner because it has reached for more light. If the rhododendron has grown more shaded with time, that's the most likely explanation for sparse flowering on the main part of the plant. Thin out the shade to let in more light if possible. Test the soil.

Look at undersides of leaves with stippling (yellow speckling) for bugs, using a magnifier if you have to. Otherwise I see a lot of blotching and premature defoliation of this variety in our area, since foliage mildew became prevalent here. (Lace bug damage can look similar, until recently I was assuming it was all mildew).

Also taking samples of affected leaves to an independent garden center - sometime like on a weekday morning, when they are not mobbed - or a USDA Cooperative Extension Service Master Gardener Clinic - where you can get somebody to view and discuss the involved syndrome(s) in person might be something to try.

You do have some flower buds in the shrub that still look viable.