Googled it few different sites sell the gel. YouTube has instructions also. The sensor has a layer of gel that actually contacts the glass and sits between the glass and the sensor eye. Sometimes they do get dirty. Or just from mileage they develop bubbles in the gel. Or from having windshield changed buying installer who doesn't redo the sensor and tries to use the old one. That's a No-No I think that's what happened to mine. When you look into the sensor it should be clear. Mine had bubbles in it and when I took it off it was filthy. Had to clean it out with alcohol and then fill it with new gel and install as directed. They give you good directions wasn't too bad. Works perfectly now.