Thank you for attaching the image of the damaged leaves on your rhododendron.
The rhododendron is not sick. Instead, those few leaves were sunburned last year.
To prevent a repeat of the same thing this year, water the shrub at least once a month, to about 8 inches deep.
And add mulch underneath the canopy to help retain moisture for the shallow roots. Choose between 3 to 4 inches of bark chips or 2 inches of bark dust.
Enjoy your garden!