Flashing 4x4 light

Had a strange occurance yesterday morning when out and about ... After running the Jeep in 4H for quite a long time ( did about 20 miles across ploughed fields and very soft ground )... and then Fording a few rather swollen rivers (water up to door handles and bottom of the windscreen in places ..) we made out way along some roads. Dropping out of 4wd was fine, but when selecting 4wd again, the selector slipped too easily in, and no light came on ... out and in again, and then the 4x4 light started to flash.
Stopped the Jeep, put into 4L and everything was fine ... low ration engaged, light steady.
Stopped, and back into 4H no probs, but when dropping back to 2wd and then into 4wd again, had the same problem.

... had to use 4L at another point and from this point onwards, 2wd --> 4H worked fine .. Light on constantly as it should.

what do you all think ? build up or Mud . much on the selector ?
weak spring ?

Sounds to me like it may be water in something if you had it that deep it was swimming, possible some mud/silt in there too.

This is what I thougt ... Mind you, at one point, I did turn the snorkel head backwards as the water splash went literally over the roof !!

Just been out and it seems to be working ok, Hubs still work, as does the 4wd system