'73 318 how do you know if original engine mount rubber is good?

I'm considering repairing the old ones with silicone/urethane. This seems like a great idea. Is this as good as getting new rubber? Does this remedy last or is it a temporary fix?
No Sir, the additional material add to New Rubber will make em a Lil tighter, and stronger. At least you have the good mount set up. My 68 Coronet had the older biscuit style, kept shearing em off, even broke a torque strap! Gotta Love big block Mopar and a 4 speed!