Sprinkler Valve Ease: What's Normal?

Hello,

I received a VP37 with a leak.
While disassembling it, I noticed that this [item] has been taken apart before.
sealed with contact adhesive.
During the process, some material also ended up on the cylinder bore of the injection control piston.

I cleaned these, and now the injector nozzle valve can be moved.
Slide it back and forth with your two thumbs.
It's not easy, and after pushing it a few times, the effort becomes painful, but it doesn't get stuck, and the track still looks good.

Now, my question: Can the piston be this difficult to move, or should it be able to be moved with less effort?
The pump is still assembled, so the lifting disc is pressing on the roller ring, which should make it more difficult for the roller ring to rotate.