I have a front walkway with similar problems; I'm up the road from you in
Aberdeen. I pulled out one of the boards a few years ago when I wanted to
run wires for acccent lighting under the walkway. It went back in without
problems, I just tapped it into place with a mallet.
While most of my boards are in good shape, some are rotting out. They don't
look like they're standard thickness, the carpenters who build the walkway
probably ripped a cedar 2x6 or larger stock. I'm planning to cut
replacements from 4x4 fenceposts. I don't anticipate any fitting problems,
cedar is soft enough for a press fit.