1. Paint the insides of the screw holes with white PVA wood glue, diluted 50/50 with water. Allow to dry.
2. Make a paste from fine sawdust and PVA, with just enough glue to bond the sawdust. Pack the holes with the paste, allow to dry thoroughly (preferably overnight).
3. Drill a small pilot hole for the screw.
4. Fit the feet using the screws.
You could also consider repositioning the feet so that they still cover the old holes, in which case omit steps 1 and 2.
Possibly -
5. Coat the tops of the feet and the corresponding surface of the cab with a thin layer of contact adhesive, and allow to go tacky (see instructions).
6. Place feet firmly in position and replace screws.
However, you would need to be sure that there will be no adverse reaction between the adhesive and the black cab finish, so -
7. Talk to Alex!