23 Self-bailing deck history ?

[RS]

FWIW, my 20' 1979 MA drains through the transom, while a buddy’s 1978 drains through the bottom. According to the hull id, my outer hull came out of the mold in 9/78, while his was struck in 5/78. I know you asked about a 23, but I thought this might give some insight anyway.

Also, I think the sinking issue could be from water getting past the hatch in the splash well and into the bilge. That area is usually wet from wave action at the stern.