hi bruce
as hanno suggested, going with the regular fluid is probably the safest bet. having said that, the manual i refered to was released in 1982, so i can only asume that's when the conversions were going on. when i made the reference to older vehicles i was thinking of first series m37's, m34's, and m151 / a1's, which may have survived without a rebuild since new. if your vac booster is only ten years old, it should work with silicon fluid, but in light of where it is located on the vehicle, and servicing requirements......the safe road is probably the best road.
mike