DeLonghi dishwasher mod DY5S type 1205 poor washes!?

Having problems with poor washing performance especially on the top wire shelf. The rotating washing arm has very free movement and always has water in it following any wash cycle. I sort of get the impression final rinse's are not being carried out as lots of debris is retained on the cups/small plates and breakfast bowls. The machine won't let me observe with the door open so I'm a bit stuffed on this issue. We very often have to wash these by hand. I'm tempted to change but it's built in and I don't know what kind of a job it would be to change the front door panel.