Just in case...
I thought I needed a pressure cap. I kept having
antifreeze show up in the pan under the
engine. Until I called Trans Atlantic
Diesel. They told me to not fill my 4.154 (with Bowman) so full. I stopped filling up to the top & now I don't get any more
antifreeze overflow.
Your cap may indeed need replacing but you might want to check the level of fill.