Brake pedal rod for master cylinder - which to use?

As I understand it, the sole purpose for the rubber retainer is simply to prevent the push rod from popping out of the back of the piston if your foot slips off the pedal and it snaps up. Otherwise, when will there ever be an upward force on the rod???

As a simple substitution for the retainer, I was told to squeeze a glob of RTV silicone sealant into the cavity and seat the rod in there while mounted to the pedal. Once the RTV sets up, it will have the rod captured, the machined groove in the piston filled, and, in effect, lock everything together. There you go, no popping out of position and causing great excitement.

Anyone ever do it this way?
Jerry