Sealing multi dimensional cracks in the shower

One of the first projects I tackled after moving in was the shower walls in the bathroom. Before there wasn't a shower, just a bathtub. My cousin had already installed the shower head but never did anything to the bare wood walls. He had the panels there at the house but never had a chance to put them up. I finished out the shower, following the instructions to seal all seams and thought I did a decent job at it.

Two years later everything that I did still looks great but the panel itself has developed tiny cracks in the decorative tile pattern in the "grout" lines. This is either because my bathroom sits in a doorway to another dimension or because the decorative coating is thinner in those areas. Not wanting to risk something escaping through the cracks into our world I asked Andrew at the hardware store what he would recommend to seal of these tiny portals.

Spent a couple hours caulking these grout lines to temporary fix the problem. This was only to prevent further damage to the walls, once I get caught up on a few other projects I'm planning on tearing the panels out and replacing them with fiberglass panels. Our maybe actual