The problem with aluminum and stainless threads is, if they aren’t kept well lubricated, they tend to gall. Being used in salt water doesn’t help them either. This galling can build up inside the transom clamp literally welding or jamming the parts together. Unfortunately, no amount of heat or penetrating oil can now release the parts. Drilling out the old clamp screw and chasing the existing threads will prepare the clamp for the new replacement part.
Here’s a Johnson JW clamp I was working on today. The threads were badly galled so cutting it to remove it was the only solution. Making a replacement part isn’t too hard to do.
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