If the O-rings aren't going into the bore at the bottom, you'll never get a seal. The O-ring type worked for my flaming river rack, but it's brand new. An O-ring bore has to be smaller than the O-ring O.D. or it will not seal. Enlarging such a bore would be a tough job to do properly, without taking the rack out and putting it on a Bridgeport or similar small mill.

You'd better research the proper interference fit before any machining is done.