For a shop workbench i would put on a thinned coat of polyurethane varnish.
Finishing a woodworking bench. A relative of mine wanted to know what finish is best to use on an outdoor oak bench he intended to make. Varnish will probably offer the longest most durable life. Otherwise skip to the next step which is to apply several coats of oil based gloss polyurethane. Nothing blocks uv rays better than pigments.
This rig serves as the assembly bench in the popular woodworking shop but if you put a vise on it somewhere it probably could serve as a workbench in a production shop. When working with a softwood workbench top such as plywood many woodworkers find it important to add a finish to the workbench so it is easier to clean as well as help the plywood last longer. Since plywood is a softwood it is much easier for liquid oils and other residue to get into the wood and cause damage. Not much will stick to poly and you will certainly have spilled glue oil nondescript goo and other things on the bench over the years.
Was it spar varnish or is there something better. In my own case i built my current benchtop more than 35 years ago. A teak bench holds up well outdoors without a finish. You can finish the other surfaces of your bench however you like with whatever finish you prefer.
Dyes impart some color to the finish but do little to block uv rays. Once damaged wood fibers separate from the underlying wood taking the finish with them. If you are really going to do actual work on that workbench top then it won t look pretty very long. Build the finish until you like the look and enjoy your workbench.
If you have installed some big dents or surface distortions over time you can renew the surface by planing it flat provided the surface is thick enough then put the oil finish on once more.