As mentioned, roughness average. It's the method of measurment of a surfaces finish. You can polish/lap the individual faces of each gear, or pay to have it done to fix it if in fact that's the issue. However when they're assembled like that (probably still if they were disassembled simple do the number of involute profiles) it would be prohibitively expensive compared to just buying a good GM 5 pinion planet.
If the RA value is bad, it's something that should have been done at the factory. If it's not, its a possibility that's step they're skipping or skimping on to meet the cost.
