We have a 3 year old De Dietrich integrated dishwasher, which up until relatively recently gave sterling service in terms of performance, but I'm having problems with the machine lately. Dishes in the top tray are no longer "clean" after the wash cycle- there's nealry always a small residue of dirt baked onto glassware and crockery after each wash now. It's very annoying. I've tried using a more intensive wash programme, cleaned the machine thouroughly, checked the arms for blockages etc. All this without any noticeable improvement. I'm stumped. Does anyone have any other ideas? Some of the dishes are pretty old I suppose (glaze is dull etc), so I'm wondering does this affect their washability (maybe I need to replace?). There are no plumbing or waste issues.