This is one of the very few instances where I'd use cyanoacrylate glue
on plastic.  The glue sticks so well to rubber that it's the adhesive
included with drive belt kits for repairing old VCRs, phonographs, and
tape decks.  Just make sure the surfaces are perfectly clean (use
alcohol), and don't waste time spreading the glue -- just apply a drop
and attach the foot to the case.  One CA manufacturer's training
emphasized that the faster the bond was made, the stronger it was, and
they instructed against wasting time spreading the glue, even in the
case of a certain aircraft.

Rubber/contact cement comes in different qualities, and I've had the
worst luck with the kind sold among the office supplies, such as
Pliobond, and the water based type made mostly for laminating Formica
to countertops.   Automotive weatherstrip seal works well, as does disk
brake anti-squeak glue sold in squeeze bottles (not aerosol).