Fortunately the workmate parts I sliced were the wooden top board and the plastic spacer.
Time to make another.
The first important measurement you need to make your life easier is the kerf of the saw blade you just sliced the workmate with.
The original board was a piece of 124mm x 600mm x 15mm block board. I have replaced this with MDF and only had some 18mm in the shed so had to recess the plastic spacer blocks.
Using the original board as a template mark up a new board, simply clamp it on top leaving the kerf space were it was cut. Measure the hole sizes and use appropriate sized drill bits to mark through the original board (I needed 8mm, 13mm and 20mm). Now with all the information transferred cut out the board and drill the holes. I used spade bits and find to miniamlise break out drill 3/4 of the way through and finish from the other side.
As I was using 18mm MDF not 15mm Block board I need to route out and area 3mm deep to fit the plastic spacer blocks into and allow the top to be flush with the other workmate original board. The sliced block was glue to the new board and also a piece of wood was glued and screwed to the broken block for strength.
The edge of the joining side needs a grove cut down the length were the to boards clamp. This was done with a router and a oval cutter bit.
Finally the board was given several coats of varnish for durability