Rubber seals on halides? Are you talking just around the wire connections, or the bulbs themselves?
I'd be leery of anything rubber being near the halide bulb... could be a fire hazard.
Neither of my halide bulbs have rubber seals, though I do have rubberized endcaps on my PC bulbs and the wire nuts connecting my mogul halide sockets are siliconed.
Maybe I'm just not understanding correctly... (which wouldn't be the first time)
