The hole in ther center tube is tiny, about 1/16" in diameter or so. It's not too uncommon for it to get plugged up. Screw the top cover bolt into the tube and apply air pressure to the bottom fitting hole. That should blow any debris out of the return hole in the center tube. Oil from the side fitting enters the housing, passes through the filter element, and exits through the flow control hole to the fitting at the bottom center. Keep searching- - - -the exit hole has to be there.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!