Nikkormat FTN, Shutter release 'waits' till I release the shutter button

Acquired an FTN and it has a problem.

clicking the shutter release button works as if I am 'bulb' mode.
That is, it waits till I release the shutter button, and only then the mirror goes back down.

Is there a spring or something that's supposed to 'finish' the shutter work without waiting for me to release the button?

I opened up top and bottom, applied electric clean, than a bit of light oil, then clicked about 100s or so (many times engaging the timer, as with the timer it releases correctly and shutter speeds seem to be ok).
But it is not helping yet.

Would appreciate any guidance/suggestions.

update on my side: after actually using film to put through the camera, may be 10 times, the problem went away. So I am guessing that my earlier 'clicking' was not enough, I had to put film through to get all the gears working