With these syringes, there's a difference between operating stifly and smoothly, versus stifly and jerky. Most of my syringes are stiff, but work smoothly which is fine. However, a few of mine, mostly older ones, are stiff, but jerky. The jerkiness isn't so bad when filling cartridges, but if I'm using it to refill my OEM Epson Workforce cartridge, it's a problem because I don't want a sudden jerk to blow any internal seals. The other syringe that operates jerkily is the small syringe I got from IJM with the head flushing kit. I don't know why, but I cannot injet piezoflush smoothly into the head manifold and it makes me nervous that I'll blow seals inside the head because of it. All other syringes I got from IJM are stiff, but work smoothly after a year.
I suspect piezoflush (and hot water as Walker says, but I haven't experienced that) may remove some of the natural oils in the rubber plunger that make the syringe work smoothly. Some one mentioned to me that as they get old they become sticky or jerky.
For cleaning syringes, I bought a baby bottle rack and let them air dry for a couple of days before putting them away. I store the barrel, plunger, and needle in a small plastic bag once dry, separated as Walker suggests.