If you're getting baked on dirt on the top shelf of your D/W I had this problem with a Bosch (mostly noticable on the inside of glassware) and I fixed it...
I searched around on the web and found a lecture from an appliance engineer - hard talking but logical...he claimed...
The dirt on the crocks can only come from food debris we put into the machine ourself - it pays to rinse off the worst before loading - weetabix, eggs and mashed potato are some of the worst offenders.
It pays to load the machine so that all the crocks get a good splashing. Cleaning the filters and checking the spray arms helps. I ran an empty load with a couple of cleaning tablets in the cutlery basket. Always keep the salt level up.
The greatest help beileve it or not is Rinse Aid. It appears that this stuff is not to make the dishes shiny but to reduce surface tension in the water to allow it to drain off properly - any droplets on the crocks may contain tiny bits of food crud and if they don't run off the steam heat in the drying cycle bakes them hard on.
Instead of using the cheapest rinse aid I went up-market and increased the dispensing adjuster for it. Now I always make sure I have plenty of this stuff in the machine and my dirty crocks problem has gone away.
