If they were sintered they may have been OILITE..in which case, a drop of oil every 3 years should keep them going for like.. hmm the ones on the bike outside are 38 years old. Benn riding it 2.5 years plus.. time to oil them..
I have encountered a set that were coming apart.
Another person rebuilding a set of cabs discovered the same problem and I was able to help that person too.
Since you doubt me I will now post a photo of what that bushing looked like upon tear down.
Here is a bushing that has come apart from corrosion.
The problem is caused by a bronze bushing inside of an aluminum casting. There is also a pin inserted into the bushing and that is a steel pin. Fortunately the steel pin usually gets completely corroded and it makes it easier to get apart.
Also the steel throttle shaft gets a lot of pitting corrosion in the area between the sets of bushings. Otherwise between lifter arm A and lifter arm B.