I had the same issue. My car does not have the factory correct antenna, but does have a small rubber seal/grommet that was worn, cracked, not seating properly between the antenna base and the fender. The few times I did get caught in the rain water kept coming in under the glove box by passenger feet. Replaced the rubber seal, no water coming in. I'm not sure what the correct factory antenna mounting is like, but you may want to check.