We have a Polti Vaporetto and I agree it's great on carpets, floor tiles, tiled walls, etc.
However, when I tried to clean the really mucky club loco and, at another time, the alloy wheels on my car, I found that the steam immediately turned to water and it was useless for these tasks.
Try some solvent – eg caustic soda or paraffin with the usual precautions – and a bit of El Bow grease.