I've got a small problem with my dishwasher - as advertised, sometimes
the
soap is still there in the soap cup after I've done a load, just sitting
there in a big lump. The little door opens up, but the soap doesn't go
anywhere.

Load the dishwasher properly so the spray arms can rotate freely. Sounds
like the spray isn't getting everywhere in the washer. Could also be a
plate/etc that you're putting in that blocks the spray from the door.

The only other thing is that the seal on the door is letting water in and
making a sticky clump. Considering what a dishwasher needs to clean, this
shouldn't make a difference.