I have a Delta single handle shower model 602 that does not have much pressure to either the showerhead or the spout. It is approx. 27 years old. I have replaced the ball assembly and the seats and springs and cleaned some hardwater deposits form the fixture itself. I have also removed and cleaned the diverter assembly and it seems fine. I can't figure out why the pressure is low, there are two double sinks in the same bathroom, two double sinks and a shower (same Delta fixture) in the bathroom in the next room. All of them have good pressure. The low pressure is in both the hot and cold lines. I find it hard to believe that both of the lines could have some kind of blockage. I’m thinking maybe the fixture itself is bad, but there aren't any more moving parts to replace. Is there a way to clean out the inner water pipes of the fixture to clear a potential blockage? Any suggestions?