How to water proof chipped concrete around garage door
The Loctite PL seal you want to use is good for a crack depth up half an inch according to its datasheet. Since this a window-like sill, if it was properly installed, it already has some kind of PU or similar foam under it to prevent water infiltration between it and the concrete. So, if the crack looks even more superficial than that half inch, you may get away with just plastering the surface of the crack with quick-set mortar.

There's no easy way to rigorously test crack depth here because any serious test setup (e.g. dye injection &amp; core drilling) is just as involved as a deep crack repair, which would involve first sealing the surface with the aforementioned mortar and then injecting a PU foam deeper using injection ports. I don't suggest using this method until you have an actual leak (which insofar you didn't see).

Also, ultrasonic crack depth measurement (for which you can rent equipment) is fairly difficult to apply here because the crack is very close to edge of concrete and it is going to have to deal a other unknowns like whether the cavity under the sill is filled with some foam which has lots of air bubbles in it. You might as well take the sill off and take a look.