I have an Oliver baler, but it is a little newer (but not much) than the one you pictured. Mine feeds the hay into the chamber with something like a 4 bar rake and fingers pushing it the last foot.
Mine works great, but each year it takes about 100 bales run through it to get everything shined up and smooth again. Once that much hay is through the machine I rarely ever have a bale not tied.
The biggest issue I have is with a light windrow, the hay does feed to the "far side" of the chamber (away from the pickup) and the string on that side is then a little loose. As long as I keep the windrows size right or speed up through the field the bales are a good as any.
The knotters are largely the same as most other balers and not an issue to get parts. I think the AGCO dealer near me was able to get the exact billhook for my knotter I needed off his shelf. Parts like sprockets, chains, etc. are available at TSC or NAPA. If a larger part were to break on most any of these older balers, I'd guess most of us would be looking for another baler.