After stripping the flooring to the bare concrete slab, I removed the
wood trim at the bottom of the wall. There is an irregular 1/4" gap
between the slab and foundation along the complete length of the outside
walls. Most likely, the gap is due to shrinkage over the 40 years since
the house was built.

I'm planning to install a Pergo-type laminate floor over the recommended
vinyl vapor barrier. I'll extend the barrier up the walls 1-1/2", so it
covers the gap but will be concealed by the new floor molding. Should I
fill the gap, with caulk or some other flexible material?

Thanks,

Ray