I just bought and installed a new replacement (4-piece) Sterling shower unit with Vikrell walls. A slight surface dimple/indentation (5 mm in diameter) was discovered on one of the walls after installation was complete. The crack has not gone all the way through the shower wall.

How can I fix/repair/seal the crack so it won't leak before I use it?

There are several products on the market to fix this sort of problem, you may have even seen them advertised on late night TV. Here is one made for Vikrell (http://www.surface-repair.com/diy-sterling.htm)