Skimmer keeps overflowing

[jaBX1]

So i have had eshopps psk-100 for about a 1.5 yrs now and its always been great for my 29 gal (35-40 total water vol). I usually have it dialed in so that its a medium consistency skimmate and would empty it once, maybe twice, a week.
recently after a few days of running and there is some gunk on the inner neck i wake up to an overflowing skimmer with water on the ground.
sometimes i get lucky and i hear the collection cup lid rattle and shut it down quickly. (today i was not so lucky and water was on the ground.

not only does this add all the skimmate back to the tank but i am nervous to leave my tank for extended periods of time.


anyone had this problem? and how do i remedy it and get it working like it did.

Ps. i live in an apartment so water overflow is a serious no-no

 

[jaBX1]

i cleaned the skimmer (soaked in water/vinegar sltn overnight) about a month ago. it took a while for it to not spray micro bubbles everywhere but is good now.

I did not soak the collection cup though. I am thinking this could be the problem as there is a permanent light brown color towards the top of the neck that wont leave even when i clean it.