u/Background-Fig-8903

I Should not have gotten this stone, obvi. Over the past year or so, a crack developed in the stone, behind sink, and is about 8” long now. Seems to be widening, too. Today I saw that a whole chunk had come loose. Bottom of chunk is rust and there’s the a cylindrical “imprint”. In the hole it Looks like there’s a rod or something that rusted and expanded underneath. Is this a natural iron deposit, or a support that was added when they installed? Countertop was installed about 8 years ago.

I'm installing a shower beneath a sloped ceiling, and hope to raise the height of the shower head beyond the partial wall containing the plumbing. Most reviewers like it, a couple state that it is un-tightenable. Any one with experience here? Also, would Locktite be a fix if it does droop?