We just repaired our grab rails on our 1975 Ericson 29 and may have some advice that would be applicable to you. The originals were held into special nuts that were somehow embedded in a hole in the outside of the cockpit. These had rusted, several had dissolved completely, and all were letting water through between the hull and the headliner. We removed all the bolts (1/4-20) that we could and then carefully used a Sawzall to cut through the teak as little as possible to sever the remaining broken or frozen bolts. We kept the original embedded nuts where possible. For those weakened or missing, we carefully pressed a screwdriver through the hole from the topside, just enough to push on the headliner inside in order to mark the position. I then cut neat 1 1/2" holes with a forster bit. Then drilled a 17/64" hole through the original fastening hole, put silcone sealer on each foot of the rail and liberally in the holes, and through-bolted the missing ones, using a SS fender washer and nylon-insert nuts on the inside. I then used a Dremel with a diamond rotary blade (cheap disks from Harbor Freight) to carefully trim off the excess bolt (each was a little different). Finally, some nylon electrical box plugs (from ebay!) filled the 1 1/2" holes. It leaves a series of dots on our ceiling, but easy to pop out the plug for inspection or repair. They now seem secure and watertight for the first time in years.
