I have a situation with my 2017 Colorado diesel. When I added DEF last time it did not hold the 2-2.5 Gal jugs I bought, so I had about an inch left and the tank was full right to the top. Today I decided to put in the last inch from the almost empty jug. The little cap just strips. I imagine the corrosive def dried and stuch the cap on tight! How to fix? nothing seems to work!