Unlikely to be getting in from the rudder as that is a 10mm tube moulded into the hull much the same way as the keel box. Then the plastic inserts are added top & bottom to hold the rudder post.
Much more likely that when you dropped it you have fractured around the keel box. This is a known weakness on both 65's & 95's, although more common on the 65's.They tend to be hairline cracks & can be very hard to see.
It is also common for the deck hatch to leak unless you use good quality tape & ensure it is 100% stuck down, especially at the tape overlaps.
Best practise is to seal up the hatch & pressure test the hull using soapy water to detect any air leaks, you only need 2 or 3 psi. I usually attach an air line to the drain hole, but you can use a straw & blow too.
i was lucky with my 95 & found no hull cracks, just slight leaks around the hatch tape (which i would have sworn I had stuck down 100%), the sheet pulley & the bellows. It is amazing how much water was getting in through these tiny gaps.