That lever is spring loaded by a spring under the cover could be it broke or jumped out of place
Out of curiosity, how and where do you intentionally add oil to the air system. Makes sense. I have an issue with my shutoff air solenoid too. It's finicky, usually after a goo 2-3 hour run it won't want to shutoff. All it takes is a tap on the solenoid for it to popout.
i just take the hose off the clamping cylinder and put a small squirt of light oil in it directly...i am not sure every part of the air system likes oil...on second thought, yes, i am sure.
Your assurance has come into question. There are different types of oil. Engine oil is bad for air systems, but air tool oil is good for the stop clyinder.
I'd stay away from 3-in-1 oil for anything of value. I used to restore antique sewing machines, and one of the '3' components in 3-in-1 oil will turn to varnish after being exposed to heat and time. Nearly every machine which encountered 3-in-1 oil in its life had to be soaked in kerosene to break the mechanism free of the varnish which formed.