Not sure. It may be grease to keep it from rusting inside. Maybe have to contact a shop and ask. My 22 year old nephew did it, but haven't seen him in over a year to ask him. Sorry. I had a mechanic mess with it and he couldn't fix it. This kid fixed it all by himself! I guess they do tend to get stuck in the hole with all the road dirt. I wish I could be more help to you.