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I have had this problem with the cheap hydraulic switches, but that's only on 64 1/2 Mustangs. 65 on they are mechanical. There is no bolt, just the pin on the brake pedal. The master cyl rod has a flat on the back that works as a rocker switch. There are also some plastic spacer/bushing as I remember. When this happen to me, I had put I think it was a 69 switch in and when I went to the 66 one the problem went away. Kultulz is a good parts man on here, maybe he can show the different part numbers.
Still thinking about it some more, I have also seen the pedal assembly bushings that hold the pedal, completely worn out and eating into the softer metal in the housing were the pedal goes. Check to see if that is not worn out. The inserts in the pedal assembly are not replaceable, but the plastic bushing are.