You can directly clean the Ultem & PEEK parts with acetone.
If you feel like the acetone is too strong, you can dilute it with water.
Diluting acentone is also more economical and create less odor.
The Ultem & PEEK parts have superb chemical resistance.
Unlike the typical plastics used for most of the fountain pens, acetone will not react chemically with Ultem & PEEK, especially when it is used for a short period of time (cleaning).
Also, Ultem is impervious to ink stain unlike general transparent plastics (acrylic (plexiglass, resin), polycarbonate, etc.)
This is the reason why typical transparent plastics are not used for Eureka pen parts that require transparency.
