Use an o-ring to convert your Platinum Preppy and Platinum Prefounte into an eyedropper pen (silicone grease sold separately). This pack contains four o-rings.
I followed the YouTube videos to convert my Platinum Preppy into an eyedropper pen. Slathering the silicone grease on the threads along with the O-Rings sealed everything up. Just check on leaks every few days/weeks to re-apply the grease.