I would try something stronger than either. Silicone is way too soft to stand up to pressure. I don’t know enough about JB weld, but have only heard good things. You may want to contact a local supplier of plastic resins and see what they recommend. Fiberlay is one supplier with awesome support. Some of urethane compounds have a high volume of aluminum. It is not expensive in small quantities.

Were it me, I’d try some quick dry urethane first and if that didn’t work, I’d use a sleeve and re-cut the rack side to fit. As another and probably better alternative, you could widen the hole on the rack side and cut in a sleeve that matches the existing screw side. If that failed go for a replacement rack.

If you go the route of applying a resin, clean everything really well with lighter fluid (my favorite cleaner) and paper towels. Use lots of ventilation and a fan while cleaning.

As another alternative, you could pull the rack and take it to a machine shop. A competent shop could rebuild the threads so it would be stronger than new. That would still be a lot less $$ than replacing the rack. Unless it is showing other problems…

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