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My drain tubes (1979 22' Revenge) looked good with a quick visual but they were allowing water entry (moisture measuring tool by a boat surveyor). Once removed they were failing from the inside out. The foam side was failing but they looked good. I installed the new ones with the tubing and o rings from McMaster Carr with a generous amount of Boat Life/Life Seal. I delicately ground the outer flange and tapped out the tube using an extra small piece of the replacement tube as a driver. Do buy extra tubing, you burn some up with mistakes. I tried collapsing the first one for removal but it distorted the tube and I was "sweating out" damage to the gel coat. Once you remove the tube you will be surprised just how thin the gel coat really is. I would not use sikaflex because of its adhesive properties. Stick with sealants and the o ring. I would contact Boston Whaler directly......I do not believe they would recommend sikaflex. You try to replace or work on them in the future and you would run into problems.