My slip trolley has been in operation for almost 5 years. In all waters of Europe. With sandy beaches, salt water, dirt and frost. Everything that plain bearings don't really need. The result is that the axle is almost sanded through and the sockets in the wheels now have an inner diameter of 28 instead of 25 mm.
The sockets on the wheels can be replaced, one costs just under one euro. I've bought a few, but I'm happy to pass on the address.
The other major problem is the axles. They are welded to the frame and are much worse, the axle part can be dismantled, but not bought.
The solution: There are aluminum tubes in all possible strengths and sizes on the Internet. I once ordered one meter of each.
20mm solid material or 20mm pipe fits into the axle segment. You can then slide another sleeve onto this tube, which has 20mm inside and 25mm outside. And the bike fits on it again.
The broken stub can simply be neatly cut away with the Flex. Be careful not to let me cut into the square tube. Then grind smooth with the grinding wheel.
The new pipe is pushed in and fixed with a screw. For this I cut a 4 mm thread in both parts. Advantage: The whole thing can now be easily pulled out and thus the slip trolley is much narrower and you can e.g. also put on the roof rack with the modified segment.
Here are all the pictures for the project: