A pen having a printhead and a chamber for holding ink; a sensor for monitoring changes in the amount of ink in the chamber; and a pump for seletively drawing ink into or expelling ink from the chamber. The system comprises a lower chamber and an upper chamber sized to fit within the lower chamber. Each mold includes upper and lower mold sections, with at least one of the mold sections being moveable in a non-circular first endless path, and being moveable with respect to the other mold section to form a mold cavity. The loop material of a hook and loop mechanical fastener is a particularly useful retainer. The elastomer bushing has a bulged outer surface portion extending continuously and uninterrupted outwardly of the angled transition portion and extending continuously and uninterrupted outwardly of the step portion.