Improving/repairing tiled fireplace

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My fireplace is not magnificent but it is original mid sixties and we quite like it. The grouting is discoloured and will not clean up any more. A few tiles are cracked and one has had a repair with grouting that just makes it look worse now the grouting is darker than the tile.

I know I can re-grout and paint the tile to blend in a repair but I am a bit hesitant to get stuck in, and make it all worse...

Any experience?

Daft thought , but what about removing cracked tiles and having random insert tiles?

The damage is not so bad to warrant that. I think damaged areas can be improved. I just don't have confidence to tackle it.