MD, I patched up my daggerboard wells on my 5.2.
They had worn through at the back, lower end, probably from repeated beaching. I tipped the fully rigged boat on its side (can be done solo, but requires a leap of faith to grab the shrouds before the mast goes "Dong"), cut three layers of biaxial woven mat (45x45 degrees)to size (stepping up from lower layers with an inch of overlap to the damaged area to a top layer with two inches approx overlap. Cleaned the area out and sanded with paper on a stick. Then mixed some epoxy, saturated the three layers and the damaged area, draped the patch over a thin stick covered in duct-tape and applied to the "wound". The stick was actually two mixing sticks taped together. It can be used to put pressure on from inside. I then let it get an initial set and turned the boat over to repeat on the other side (which was also worn through and previously "fixed" with PU sealant (thank heavens not silicone!). Tip: do not place your cup of excess epoxy on the hull to cure, it will burn your gel coat!
NB: my daggerboard wells were otherwise structurally OK or I would have had to reinforce them from inside (bummer).

Good luck!