I just did mine. I re-bedded using Butyl tape, available at most auto parts stores. It comes in a roll that should last you about fifty years.
Start by removing the stanchion and clean off any old sealant. You might also re-drill the holes with the same size drill bit, just to clear out any old sealant. Also, countersink the holes so that the Butyl tape can fill them in and seal better.
Apply the Butyl tape to the bottom of the stanchion base, and be sure to wrap it around each of the holes. Also wrap the tape around the top of each bolt before you install them. When you tighten the bolts, hold them in place on the outside while someone turns the nuts for you on the inside.
You should notice the Butyl tape squeezing out as you tighten. One of the nicest things about Butyl is that is super easy to clean up...simply pull off all that squeezes out. Use the excess rolled into a ball and dab it on any areas where the Butyl has left some remnants, and it will lift it right off.
Nothing that I have rebedded has leaked yet, and I have confidence that it won't soon, either. But if it does, it is really easy to clean up and re-do it if necessary.
It's not a bad idea to put some washers on the inside. I normally use the normal size washer for whatever bolt I use, not an oversize or fender type washer.