Sink popper won't work when stopper is on?

[CNorts3]

Hi all,

My sink popper will happily go up and down all day long with the cover bit taken off of it - however when the cover top is put on it goes down and stays down (needs to be pryed up)

Images below if someone is able to diagnose this and let me know how to fix or suggest the name of the product i need to replace this?

Thanks in advance

 

[Madrab]

It's not going down far enough to click the mechanism properly, possibly the seal has hardened up. Put some silicone grease on the seal and see if that makes any difference.

 

[jeff the gasman]

Or Vaseline