Use dielectric grease. It is also called silicone grease, or bulb grease. Auto stores mostly only sell it in .25oz tubes. HomeDepot shows a 6oz can for about $10 but I can not find it in the stores (order online?); or a serious electrical supply place should carry it. Will accomodate your rubber lubrication needs, as well as protect the surrounding metal from rust. I am guessing that this is the main ingredient in the Mercedes whiz-bang subframe bushing lubricant. If you go to the local parts place, just ask for bulb grease or you will get the 'deer in the headlights' look.

For you purists, the spray silicone contains petroleum distillates as propellant (probably insignificant but this is for the purists). The diaelectric grease does not contain these, and its original purpose is to seal electrical connections from moisture with zero conductivity.