To get a good adhesion, it may be better to remove the rubber completely and clean all the adhesive off the body and rubber. Then apply some sort of rubberised contact adhesive to both surfaces making sure it is evenly applied and has no lumps. Let both surfaces dry then carefully apply the rubber to the body and press down firmly especially around the edges.
It may be possible to place a small sheet of silicone based paper between the rubber and the body to make sure you have the two in the crrect place and then withdraw the silicone sheet gradually as you press the rubber onto the body. It will take a lot of care.