I found that I had one of those holes you speak of in the roof of my 2095.
We had trains running at a charity event and when it rained we kept running, but then after a couple of hours of misty rain the bogies of the 2095 showed us that they were no longer electrically linked! When opened up the circuit board inside had frothed up and etched the contact track away. A quick clean up, a blob of glue was placed where the hole was - under the glued in vent(?) on top of the body and a bridge wire over the gap in the contact track was quickly soldered in. The loco has run faultlessly ever since. (This was 1991 by the way so it was and still is good old analogue).
I often run LGB, Bachmann, Playmobil and even the odd kit built item in the rain. The only real issue I have found is the use of ferrous screws and other fittings by LGB, which is a little disappointing on an otherwise weatherproof system. They will rust eventually. Oh yes and one old style EPL add on switch had the a contact track etched away by the wet, but overall I feel well satisfied and it usually works faultlessly.
If my stock gets wet, I just empty any water out and leave it to dry. No serious harm!
James