It could be a slight variation in how the grey is made. For example, if they mix the grey plastic through addition of different colorants to the base material, and the mix is slightly off, there will be differences from one run to another. If they use a CMYK method of getting colour, then if they pull back a bit on the magenta, it'll appear more "green". If that's the case, then the whole run is going to be the same shade, so I agree with @Jdk504 in that he should source a V1 version. I suppose the alternative would be to source one of those 3P face sets and see if that helps, but it doesn't have the neutral face he's looking for.