HFS3 seems getting stiffer as time goes

I have a few HFS3s and using one of them frequently for testing purposes, and as time goes the joystick seems getting stiffer and stiffer, and it makes a lot of noise. The stiffness is not just higher resistance, but return-to-neutral speed seems to suffer as well.

However I have no problem using it at the moment, it functions well and be able to record complicated moves accurately without me banging the restrictor gate. So I don’t know if it is just a perceptive thing or not.

I guess my questions is for these kind of low grade joysticks found in HFS3s, what’s a good remedy to fix the problem without replacing the parts themselves?

get a stiffer spring.