I had this problem a few years ago and cleaned the lift. Bad move! Afterwards, it dropped like a rock. Even the thickest grease did not slow the descent rate. I wrote to Rega, and they responded that they use Roccol Kilopoise damping grease. Unfortunately, there are many different types of damping grease, and too expensive to try different types to see which works best.
I highly doubt if silicone will work. Since silicone is not a damping grease, I believe the lift will drop like a rock. Even if it did work, the bottom of the rega lift is open, and the silicone will drip out.
My advice is to go ahead and clean it to the extent of removing any pieces of foreign material visible, but don't remove the damping compound. If that doesn't work, I think replacing the lift is the best option.