Is it plausible to chisel the runner flat where the drawer has worn it then glue in some new wood? It wouldnt take much, probably 1/4 inch x 1/2 inch.
Robgil, now that is probably the way Bigwull would do it but I’m advising you not to because that would be a back-breaking long-time-doing task.
I suggest that you:
Step #1 – Make a “rail” (drawer runner) marking gauge (see picture below) out of a ¾” thick board with the length and height as shown on the photo. Now the purpose of the “rail” gauge is for “marking” the “cut” line for the height and horizontal angle of the new piece of wood to be glued or nailed on top of the worn-down part of the rail/runner.
Step #2 – cut 2 boards that are ¾” thick, …. the same
length as the “rail” gauge ….. and a
width that is less than the height of the drawer opening …… so that its edge can set lengthwise on top of rail.
Step #3 – place a #2 board on top of a rail, ….. with the “rail” gauge on the “dust” board and tight against the rail and the #2 board …… and then mark a “cut” line on the #2 board.
Step #4 – “mark it” on its bottom edge for the rail that it was cut for …. and then use a bandsaw to cut the “new” rail piece off the #2 board.
Step #4 – repeat the process for the other rail for the same drawer. Then lay the 2 pieces on their matching rails and “check” them for “fit”, first with a straight-edge or a framing square ….. and then the drawer itself. If they “fit” ….. a couple small nails will hold them in place. (and be sure to put paste wax on them when done)