That looks like fertilizer damage. Fertilizer burn is generally at the ends and edges of leaves and will be on any area of the whole plant, not just on the sunny side. Give as much water as possible to wash fertilizer out of roots. Make sure there is good drainage. Rhododendrons don't like wet roots.

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Fertilizer Burn

Your leaves don't show any chlorosis which is what alkaline soil causes.

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Chlorosis

ok i've repotted it in proper acid soil. but i'm still. should i have got as much soil out of the rootball as possible before transplanting?? i brushed off the outside and left most of the harder stuff as i didn't want to damage roots. i wasn't expecting miracle cures, but i've noticed some tiny brown spotting and slight yellow discolouration on some green leaves. any ideas what this is?
thanks

I will take a while to work out. When watering, water thoroughly so that the water thoroughly soaks the material and drains out. Then let the soil drain and don't water again until it needs it. Keeping the roots too wet will cause disease, but thoroughly watering and draining when it is on the dry side is ok. Drainage must be good. Once it gets back to normal, water normally but only when the plant get on the dry side.

Drought stress, plain and simple. Happened a long time ago, perhaps last summer.

Potted plants commonly have problems simply because the roots are limited to the pot. Would do better if in the gorund.

Here is a link that might be useful: {{gwi:384542}}

Your other picture.

Here is a link that might be useful: {{gwi:384543}}

We had severe droughts here and I never saw that kind of damage. What I did see was complete branches dying. Other branches survived. When we had several years of drought here and we observed that if rhododendrons and azaleas were not watered during a drought some plants died, but others just had one section of the plant die. It seems to be the plants way to conserve what little moisture it has. Prolonged drought also weakens plants and often results in the appearance of fungal cankers on the branches of older rhododendrons and azaleas. One must prune out the affected branches to stop the spread of fungal canker diseases.

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Typical drought damage.

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Fungal Canker