the dealership complimented me on my clean install. they didnt even notice till some was confused why the others didnt have garage door opening buttons haha. That grease is to protect the sensor in its shell. there is a rubber squash gasket that slides over the sensor and then the cover is put on flush against that gasket as it snaps in place. you could use dielectric grease or regular automotive grease you will find at any auto parts store.