If the rubber is broken or cracked transversely, but complete, there may be another option. Clean up the part and use a thin bead of crazy glue on the cracked seam, then apply light pressure until set up. Crazy glue seems to fuse this soft rubber together. This repair has, for me, also saved several of the delicate faceplate grommets that often tear apart at the attachment slots.
Once the repair is made, a dab of clear silicone on the cleaned up mounting posts, will keep the rubber mount from falling off when the cowl is opened. Dab the silicone, install the mount, and close the cowl to hold the mount in place overnight.