Already done one spot with router. 8" by 1/8", and fitted a piece 2 1/2" wide in with carpenters glue UN diluted, coating the hole and patch fully. But the rest I have some 2 1/2" wide trimmings from the edges of boards after squaring on the table saw. I diluted the glue to get it to flow freely into the crack. Then coated the thin shims both sides and hammered them home. I trimmed the excess wood while wet and applied more glue to get everything to expand. For the top I may run the skill saw over a small patch 4" long or just leave it, after all it is a workbench and may be marked up soon enough. I am happy with the way the bottom turned out with this repair it won’t even be noticed if it was the top.
CHRIS, Charlottetown PEI Canada. Anytime you can repurpose, reuse, or recycle, everyone wins!