That silicone grease is used to lubricate rubber o ring seals, so I take it they put some effort in making sure it won't destroy the rubber. From what I have seen using it is practically chemically inert (like I said, years of staying in there and when you open it, it is still there, smells exactly the same, no colour change, no nada). I don't know if it's the best solution, but you know what they say, so far so good.Hi
I would not argue against schlitz's suggestion but good old rubber grease is specifically made for rubber and metal interaction and easy to get also. But either way how are you proposing getting it in to the working area. It is probably in there but just needs a bit of activation(heat) and redistrubition(turning the parts) a few times and even a bit of "tapping' with a piece of wood or rubber hammer.
Is it worth pulling the wishbone out and just getting a drill and a way of driving the inner around at a modest speed for a while both ways to 'free it up' not too fast or might get too hot inside.
The way to get good unstressed life from the Silentbloc bushes is to tighten the nut with the car at the usual height on the wheels. This may not be with 40Kg in the boot for your car. Perhaps it never has anything in there. Put your weight in the drivers seat and possibly a passenger seat weight also depending on the 'normal' usage now a days.