Don't be too sure. If it's any flavor of polyethylene or polyanything, no adhesive/cement/glue/goop will stick to it. NADA.
Scandvik has some thread size that is not 1/2” iron pipe, so they have an adapter with a washer in it to make it 1/2”. The problem is that the washer keeps getting twisted inside when you tighten the adapter. Both are metal so Marine Tex will stick to them. I like the new shower head but we have tried several new adapters and the washer just does not seem to stay in place. So if it leaks again I am probably going with the Marine Tex but if it leaks then I will have to replace the whole shower head since I most likely won’t be able to get them apart after the Marine Tex. But the good would be if it doesn’t leak, it never will.