Thanks Peebee & Mudnut. Have been through plenty of water crossings without a problem. When I found the box was unsealed yesterday, & I inadvertantly earthed something & got some momentary sparks I wondered why water would not complete a circuit, potentially operating the winch (it obviously doesn't or I would have discovered that by now) - or indeed if ever needing to winch out of water whether the water in the control box would prevent use of the winch.

If I ever remove the cover again I'll use silastic when re-fitting it.