I've repaired a couple like that, Tom. I used a clear epoxy. I didn't make any attempt to further hide the cracks, but I have since thought that if one were to dye the epoxy black it it help in doing so. Especially if you left some epoxy proud of the base, on the edges, and sanded it down to base level.

As hard as these old pads are getting to find I can understand your wanting to salvage them.

SRH

May God bless America and those who defend her.