How can I fix my DH 101 Tricity Bendix dishwasher?

Glassware and some crockery becomes coated in "grit" after a wash cycle. I have tried using dishwasher cleaners; made sure dishwash salt reservoir is full and filled up the rinse aid container. None of these have really made a difference. When I come to unload the dishwasher I have to re-wash nearly half of the items! I have cleaned the small and large filters in the base of the unit. There is crud in the rotating arms, can this be removed, if so, how?.