engine mount preservative

My wife owns a 2003 corolla S with around 70,000 miles. The idler pulley tensioner arm has been vibrating and making noise. I don't have a cherry picker, or a safe way to lift the engine enough to replace the assembly.
We took it to the local dealership, and they agreed with me that the noise was coming from the idler pulley assembly. They did find however that the rubber engine mounts were cracked and failing. All told this is going to be a $900.00 repair.

I looked up the engine mounts in a Chilton's repair manual, and it recommended that a silicone based rubber preservative be used to extend the life of the engine mounts. Does anyone here know of a good silicone based rubber preservative that can do the job?

 

303 aerospace protectant works wonders on anything rubber for me.

 

I am amazed that you have to lift the engine to change the tensioner. Furthermore a 70$ tensioner + 2 rubber mounts for $900. Hell I can do that in a few hours and save myself $700 in labor. Nice to have a dry heated garage.