1999 Chevy Malibu distributor Cap/reservoir

I have a 99 Chevy Malibu its runs pretty good the only problem that i have with it is that the reservoir keeps getting a crack in the seem of it and I don't know why some people told me that it may be the distributor cap but I don't know much about cars so i wouldn't know so if anyone can please help me out by answering some questions I have Thank You