MGF - Auto transmission warning light on at start up - Ok when driving.

My MGF does very little mileage and spends a long time parked up. When I first start it up, the yellow auto transmission light comes on after
a short delay, and stops on until I engage gear nd move off. So far it has not come on during a trip or gone into limp mode.
This a a fairly low mileage MGF (22,000).
Anyone know what may be the cause?
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