You can remove the piston to clean the reservoir and replace the piston seals. If you take care of your pen, you might never need to replace the seals. The seals wear down when ink dries in the reservoir. When you pick up the pen and try to fill it with ink by moving the piston, the dried ink resists the piston, and the seals catch.
Solution: Leave your pen filled with ink or empty and flushed clean.
There are three steps:
To remove the piston, start by turning the knob at the back of the pen in a counter-clockwise direction to unscrew it from the back of the pen. There will be a bit of clicking towards the end - don't worry and don't rush. Just click your way through until the knob is free.
Pull out the tube. You might have to spin it off the piston stem.
Remove the plastic piece secured in the back of the pen, which should now be exposed. Take the little wrench and pass the fork around the base of the plastic piece. Jiggle the wrench until it seats correctly. There are flat sides (detents) on either side of the plastic piece are designed to be gripped by the fork. Turn the wrench in a clockwise direction. Be careful – the plastic is soft. If you strip the detents, you can use pliers if you're careful. You can also use hand pressure if you get a good grip. It's best to start with the wrench.
Spin out the plastic piece.
Slide out the piston.
Arrange the pen parts so you can reassemble the pen easily.
You can now clean the inside of the reservoir and replace the seals on the piston.
To remove the piston seals, work each seal off the piston. You can roll the seal out of the notch. You can also use a pick to lift the edge of the seal to get it started. A tooth pick is good. Try and keep the seal intact and for future use. These are DASH size # seals made from silicone. You can use harder seals if you want to. These are usually available at most well stocked hardware stores. You can order softer seals online at McMaster-Carr or a similar industrial supply business.
To apply the new seals, roll one onto the piston and work it to be back notch, then roll on the second one for the front notch.
To clean your pen, first remove the nib and feeds from the front, then remove the piston from the rear. Run warm water through the body to clean it. Use a dilute solution of soap to remove any stains or ink stuck to the sides of the reservoir. Don’t use a brush unless you want to risk scratching the inside walls of the reservoir. You can use a Q tip dipped in soapy water to try and remove dried ink.
To reassemble, reverse the steps for removing the piston. Begin by sliding the piston into the pen body, then screw in the plastic piece. Make sure the stem of the piston slides into the slot in the piece.
Use the tool to seat the plastic piece. Just give it a short quick movement over 10-15 degrees, and you should feel the plastic piece seat. Give it another short movement, and that's it.
If you don't seat the plastic piece correctly, it will start to spin out when you spin the knob back on. If this happens, reseat the plastic piece using the wrench and keep tightening it until you're sure it won't tighten any more without damage to the pen. If the wrench slips and no longer grips the plastic piece, use pliers gently.
Slide the tube onto the piston shaft. You might have to guide the tip through a slot in the plastic thing. Spin the tube to grab the piston shaft. Make sure you can slide the piston back and forth. Push the piston all the way into the pen.
Screw the knob back onto the plastic piece using a clockwise direction. Keep spinning until the knob starts to bind. It should pull the piston back towards the rear of the pen. Keep turning the knob until it is flush with the back of the pen. You should feel several clicks.