Frank, I don't know if you have sorted this out yet but my '86 Westi with a
Subaru engine works the same way.

The coolant light would come on after a short while and then stay on until the
ignition was turned off and then turned back on.  The light might then stay
off for a very short while and then come on again, repeating the sequence.
Cleaning of the level sensor did not help but replacement fixed it for several
years.  This happened twice in the 31+ years I have owned this vehicle.

Ed