Exterior lighting/lamps?

A persistent problem with this vehicle has been lamps working intermittently. Usually the lamp itself is okay, but it does not seat properly. I often remove and clean the connection and the socket, only to have the connection fail again, even though the lamp is okay. Do you advise replacing the sockets? A secondary and related problem is that the taillights and running light assemblies get water in them. Is a good way to seal them against this? Any help will be most appreciated.