Servicing my floor pump

[makoti]

Sefras FP200
Pulled the pump head apart, and the piece that moves in and out to allow air into the tube/tire is jammed. It will move (got that, at least) but not very freely. The center piece is metal, but the surrounding part is plastic. I suspect that over the years of using tubeless, the sealant has gotten into to pump head and done what sealant is supposed to, sealed it.
What can I use to loosen this up? Drop it in what solvent? Don't want to damage the plastic or whatever magical part is hiding in there. A new piece is likely $15 shipped, but rather just fix this one.
And before anyone bothers, this says more about my lack of taking care of the pump than it does about the horrors of tubeless, so spare us.