To be honest all that can be cleaned is the spindel, stuck in soapy water, washed with a toothbrush if required, or put in an ultrasonic if required, and change the o'rings and some o2 compatable greas.
The other working parts inside most modern guages are directly compatible.
<font color='#000080'>No main contents guage or regulator needs to be oxygen clean unless you intend to use a bottom mix greater than 40%
The tank and valve must be O2 clean if you are mixing by partial pressures simply because oxygen is added first giving an intermediate "mix" well above the recommended 40% level but this mix never finds its way into your main regulator or guage.
Of course, the above does not hold true for the regulators and guages used for stage cylinders. . .