I would try and make a replacement wood sleeve bearing and slide it into the steel housing. You could turn the outside diameter on a lathe and drill the inside diameter.
I’ve fixed up several old cultipackers that were of a simplified end bracket design, using pressure treated pine 4x4 with cross drilled holes, about 1/8 inch larger than the shaft diameter. Those last for many years of food plot usage, and never even need grease.
I’d probably use white oak to make the sleeve bearings for the style end caps that your Dunham has. Those should last quite a few years and would turn better on a lathe than pressure treated pine.
One of my neighbors dragged this 8 footer out by the road a few years ago. I paid them $ 40 for it. The frame and several wheels were broken, and the bearings were gone.
It took me about (2) hours to repair the frame, take off the broken wheels, make some new wood bearings and steel spacers, and make it into a serviceable 7 footer.
I have another one just like it that I’ve used for the last 20 or so years. I traded another neighbor a case of beer for that one, which was in similar condition when I hauled it home.
When it comes to food plotting, there really is no good substitute for these old cultipackers. I’ve tried dragging logs, railroad ties, bed springs, packing with smooth lawn rollers, and/or atv tires. With that stuff, seed germination is never close to that which I get with those old cultipackers.
It was always a pain transporting my cultipacker between our (2) farms, about 20 miles apart, so I ended up using that other garbage most of the time. Now, I don’t have to anymore, because I’ve got a 7 footer at each spot.
I’ve also fixed up a couple of 4 footers that I’ve sold to folks to use with their atv’s.