I've only recently investigated some of the suggestions posted here, thanks all. Basically, I replaced all the worn glassware and carried out a thorough inspection and cleaning of the machine itself; I also increased the dosage of rinse agent to see if matters improved. There was a minor improvement but still performance is nothing like it was when the machine was new. I couldn't find any other filters or access any other parts of the machine for cleaning. The only thing that did seem amiss was the actual plastic cleaning arm for the top tray- the plastic "bearing" or retaining clip is quite worn and I suspect that the arm may not be moving as freely as it should (it's quite lopsided when stationary). I might see if I can get this part replaced. Thanks again for all the suggestions.