The fact is that o rings are designed mainly for one-off long term fitting not frequent use as in a caravan application. Those used in this case are also of small cross section, and the act of struggling to fit the connector block does cause them to stretch and eventually break. Its no accident that these are readily available in accessory shops, usually in packs of 6/8, due to the frequency of replacement. The o ring material will determine whether it is resistant to any lubricant applied, but even if the rings do deteriorate as a result, this seems irrelevant when they have to be replaced appprox annually anyway. In other words its easier to lubricate and change the seals occasionally than struggle and risk more expensive damage.