If it's baked on dirt at the end of the drying then it's broken down food debris that didn't drain off properly after rinsing - droplets with the small particles in them are probably not draining off prior to drying.
A good quality Rinse Aid will improve things.
Make sure you have salt in the machine
Check the rotating arms for bits of jam pot labels
Clean the filters in the bottom of the machine
Rinse off big lumps of food before loading the crocks
Buy cleaning tablets and run one through the machine every few months
But above all use decent Rinse Aid - its sole purpose is to allow rinsing water to drain off the dishes.
Avoid the "multi" tablets.
Good luck...
Peccavi, November 2009
