Thanks guys, I think you have helped me get a better grasp of the situation.
I will try using the shims.

I don't see any evidence of leakage, I just like a solid foundation when I'm
doing my critical thinking and the shims should do the trick.

As a side note, it's disappointing seeing the way they build things now
without any regard for how are you going to repair it 5 or 10 years down the
road.