Towel bar is loose

I purchased and and installed part 10-133 (Door handle with Towel Bar Insert). Just what I needed. But I have one small issue I'm hoping you can help me with. The towel bar sits a little loose and can be rattled by touching it. There seems to have been some type of glue or putty to help the bar stay tightly mounted to the handles. It was all dried out when I took the unit apart to replace the damaged handle. What is that stuff?

Thanks for your help.