Stopping birds from beaking feed requires either some distance between the top of the front of the feeder, usually around an inch or two, a lip protruding inside the feeder parallel with the surface of the feed, or some sort of grid that prevents the birds from raking their beak through the feed. Not that many birds are going to be feed rakers but there will be a few.
Most of the commercial treadle feeders don't have anything to prevent raking. Grandpa feeder has the grid but no lip. The fairly new cheap Chinese treadle feeders don't have either. We rely on a 1/2" lip that extends into the feeder, parallel with the surface of the feed, and the fact that the feed will be about an inch and a half below the front of the feed lip, but once every few months someone emails or posts on our Facebook page about feed getting raked out and we send them a 10" x 1.5" sheet metal strip that just slips in place.
So if your old metal feeder had an inward swinging door try taping a strip of cardboard across the front, even just the duct tape will stop the raking, then come up with a more permanent solution later.
The only PVC feeders that I have seen that can prevent this do it by requiring the birds to stick their heads deep into the pipe, not good for the heavy combed birds. I am sure that works but of course these types aren't bird proof or rat proof.
