Isn't brake cleaner just ether? .... super rapid evaporation.

I did use the technique recommended and have high confidence it's a good move, well worth the tiny cost. That silicon does adhere like crazy to a well prepered surface. They are already installed but it would be reasonable to jack up the rear end, block or jack stands under the trailing arm so the wheels will spin at almost the same relative position as natural driving ... clean peaks and valleys again and add more silicon to existing and also to valleys where crazing has begun.