Just replaced the left side petrol tank rubber buffer and had quite a trial. I finished up carefully giving it a few short sharp thumps with a hammer to drive it home through the hole in the frame but I was hesitant doing this so near to the coil. Fortunately I got away with it. Now I've got to replace the right hand side and wondered if there was a better way to insert these through such a small hole?
Maybe try warming it up to soften it? Drop it in hot water for few minutes. Could also try a dab of washing up liquid?