Shower tap leak

[AndyMCFC]

Hi all, This thermostatic valve is dripping constantly I have removed the circlip but the black plastic thing is hard to move. Should I force it I am concerned about damaging the plastic tines for the handle to slide back on to
A plumber from check a trade said it’s not worth fixing and I need a new shower is this correct?
Any advice from a plumber would be appreciated. Thanks

 

[JohnD]

Your pictures do not show the whole thing, but it appears to be a bar shower.

For some reason they are not much good.

If the connections are suitable, you could save up for a good round mixer, which can be much better.