Shampooer g7d interchangeable with other g series...

Question

Your last posting regarding my new/used G7D was very helpful. Please clarify if I can use any shampooer on the G7D as long as it is in the G series ie..G4, G5, G6 etc. I am looking for a good slightly used unit but don't know which unit would work best. I am the one with the $75 G7D ultimate diamond. Thank you!