How do you know that the gas supervision contactor is not working? Are you assuming that because one gauge is showing the right pressure that the pressure is actually correct? Suppose the gauge is stuck and the pressure switch is correct in reporting low pressure.

I am going to assume that this contactor is not picking up and is therefore preventing the breaker form closing due to low gas pressure. The first thing that you need to do is lock out the breaker by removing all control power so that it doesn't accidently close while you are servicing it. Next you need an independent calibrated gauge hooked up to another test point to verify that the gas is indeed at the right pressure. If it is then you need find the pressure transducer/switch that provides the go/no-go signal to the control logic that feeds the contactor. Check to see that it is reporting the correct pressure, if not find out why. If it is then you need to check the contactor coil for continuity, if it is ok then ensure that all permissive contacts are operating correctly.

If you do not understand or know how to perform any of these steps then put your hands in your pockets, walk away from the equipment, call the manufacturer and wait for qualified help. An SF-6 breaker that is energized or closed with an inadequate gas supply/pressure will most likely be permanently damaged, as will any personnel in the immediate area, that's why there are so many fail-safe mechanisms and controls built in to it.