Try removing the heating element to clean it. You should be able to
do a better cleaning job on your workbench than you can inside your
dishwasher. Try things like steel wool if you have to.

Having said all of this, when I bought my house my heating element
inside my dishwasher didn't work because a wire broke, so I've been in
that area recently. It doesn't look to terribly difficult to get the
heating element out if you can get to the bolts that hold it in.