Transmision fluid leak from prop shaft universal

I have a 92 Astro and Have a tranny leak it is coming from the aft end of the splined shaft that plugs into the tranny. If i shine a light into the splined shaft and look down behind the universal joint I see light coming through a tiny pin hole dead center. My plan is to fill up (1/8 inch or so) the aft end of the cavity with silicone and put a 1" diameter pice of thin rubber over that. Any other Ideas would be gratly appreciated.

Thanks in Advance