Looks like a big old 'semi-ironclad' like 'Lord Roberts' which were once commonly planted as (street) trees in NZ & AU. Since fire is not a common issue in Rhododendron growing regions of the US, I can't specifically say I know what issues it causes long term with the plant. This plant looks generally healthy. Was it once more shaded than it is now? Depending on where you are in AU, a full sun exposure may be too much for it. Was it exposed at the roots to ash debris? I wonder if the alkalinity of ash could slightly raise soil pH, which rhodies don't like, and tie up nutrients, which would account for the slight chlorosis. In that case, LIGHT application of a fertilizer designed for acid-loving plants like rhodies and blueberries, could be appropriate.

@shaxhome (Frog Rock, Australia 9b) any ideas?

Agree that it's probably getting more direct sunlight now after those horrendous bushfires swept through so much of the state and decimated the countryside of millions of old established Eucs, especially in the Blue Mountains area where that Rhodo pic was taken.

Lord Roberts is basically something like catawbiense/ponticum X arboreum and should be ok in the mild climate of the Blue Mountains, in full sun. Provided it is otherwise happy. (Even in MY comparatively dreadful climate, 'Ironclads' bred with catawbiense will grown in full sun...though that certainly isn't true along all of the US eastern seaboard. The ones with more arboreum like 'Lord Roberts' or 'Broughtonii' are only zone 7 hardy, but are considered 'ironclad' in maritime climates. I have a Broughtonii bought for breeding or rootstock purposes...its leaves get a little singed in most winters around here, but it would otherwise grow in full sun)

Thanks all for your help. It is definitely receiving much more afternoon sun after the fires, not much I guess an be done about that.