Smack it with a hammer.
The last time I used the power down feed on the SB1028F mill it kept clicking back on even modest down force. I could put my hand against the lever with rather little force and it would click instead of feed.
Somehow the power down feed quit working entirely with me fumbling with it. Turns out I managed knock the lever out of the part that engages the feed to the spindle head. I was afraid it was broken, but nope. It was just not in the hole. After messing with that for a while I manage to get the power down feed working just as badly as before.
The cure? I took the clutch off, clamped the clutch lever in a vise, and beat on it with a hammer. Now it works. I leaned into the down feed lever and couldn't get it to slip and click. Woo Hoo!
Nope, didn't figure any of it out myself.
This video as the part about beating on it with a hammer: