The broken dial fault with the EOS 5 is not an issue.
All early EOS 5 had so badly designed dials that would break within 6 months. The problem occured when you tried to move the dial from the locked to any other position without pressing the lock button.
My newly bought EOS 5 had to be repaired by canon within the few first month's since I had it. Unfortunately mine was a grey import model so no warranty on it.
The canon repair man said that there is no way that any early production EOS 5 will survive the broken dial. But all repairs or newer EOS 5 are coming with a redesigned dial that is far more robust to break
True, mine was repaired in 1997 and works fine.
So bottom line. If a dial is broken, don't buy it. If it is working, it is repaired and reliable.