I owned two of them back in the day.
The cylinder release is pretty simple as I recall. Just a tiny coil spring that gets compressed when you pull back on the thumb piece.
Did you remove the side plate to check, or while you were cleaning it?
Perhaps that coil spring is out of place or kinked.
Also, perhaps a piece of debris fell into the action between the hammer and the frame.
Also, as I recall, the ejector rod tends to unscrew sometimes. I can't recall whether that is a factor but make sure that it is screwed all the way in.
If you do remove the side plate nothing is going to fly apart. The cylinder release and spring will then separate for inspection, and you can see if there is debris in the lock work or any broken small parts.
The action is quite similar to a Colt Python and the mainspring will work as a replacement.