I grew up with IH balers - 15 K + bales a year, no problems. Many neighbors had them as well - few had complaints - no more than any other color.
I also have a 430 with a thrower. Great machine.
Like anything, spend some money on the service and operators manuals - then read them. There is alot to know about any machine, and you can skip the aggrevation of learning the hard way, with no book to refrence .
For free is key, lol. As was stated, get the machine cleaned out, and if it is not rusted out, get some clean oil over the whole thing - and keep oiling it- time and volume is your ally. You would be surprised what will free up.
Those keeper springs mentioned are important, as are the breast plate fingers, which are often overlooked. If worn excessively, the twine will slip off, and wrap around the billhooks. Many people will blame the knotters, and they are wrong. Just look around - you can see what is worn.
Anyway, good luck! Hope you end up with a useable machine.