There are two ways to address this. You say your older flexible pen writes rich and wet. In other words, a really great ink flow. Perhaps it is too rich of a flow. Experiment by changing to another ink that is not as free flowing. Ask around what ink to use for this pen. I had luck going to Private Reserve. Always avoid inks with heavy pigments such as red, oranges and brilliant hue colors.
If ink creep still floods up into the nib the problem may be the nib, specifically the cut of the tines may be defective. If you think so, I suggest contacting the manufacturer or their designated service representative.
Hope this helps and let us know what happens.