Sounds like the same problem I have had on my O'Day 37. The stanchions are mounted on a balsa cored deck. When water leaks in, it softens the balsa and any pressure put on the stanchion will deform the deck. Someone has probably torqued down the four bolts holding the stanchion trying to stop leaks,,, causing the depressed area that you see.
The only solution that I could come up with was to remove the stanchion, open up a large area in the top fiberglass layer under the stanchion plate in order to get to the balsa, and clean out as much soft balsa as I could reach. Then fill the voided area with thickened epoxy. Drill new holes and rebed the stanchions.
