I have been experimenting with multiple layer natural cork seals. Why? because being a woodwind repairman, I can tell about how abbrasive the cork is, and having been around pens for most of my life, I know how SOFT and fragile the celluloid barrels are (and abrassion prone!)

Thing is that I have been able to reduce the tolerances needed to seal (aka how big you need the piston seal to be in order to compress inside the barrel and effectively seal!) using 3, 4 or more layers of thin natural cork. That allows me to pick less abrasive areas, with less "veins". Also, as for last month, I got a great nitryle rubber in .35 mm thickness and I have installed a 2 ways multi layer seal: rubber-cork-rubber-cork-rubber-cork (being the upmost layer rubber so it will behave KIND OF a vac fill when pulled up for the filling stroke. Works GREAT! just thought I might share.

Also I have been using 2 and 3 layers of this thin thin thin rubber for vac fils and performs smoother on the upstroke and while it's a little bit (just a tad) stiffer on the filling stroke, it fills more efficiently.

Alternating cork and rubber was used by a number of pen manufacturers for their piston seals. Nowadays it is probably better to use urethane, rather than nitrile rubber, for the "rubber" layers. I do just that when restoring Nozacs and Aurora 88s and the like.

me is one inventor

I didn't know, sorry! as far as urethane is concerned, I hate that stuff! I have used teflon sheets... (I often end up experimenting with stuff I use for woodwinds... I have to confess...)