If you see brown residues on your heating plate, this is just an indication that you may need to add use more soap to wash the feeding gears. The heating plate is made or stainless steel, under typical sterilize and dry operation, there is no chance for the stainless steel to oxidize and rust. The brown residue is most likely the residues from the feeding gears get melted during the steam cycle and flow down to the heating plate and eventually got burned due to the overheating.
How do I clean it?
The brown residue can be easily cleaned following the descaling steps. If you see the brown spot that looks more like a pinhole size rust and can feel a small indention to, it actually may be a case of pitting stainless steel due to long exposure to an acidic substance.
How do I know what may be the cause?
First, try descaling the heating plate back to the flawless state. Then run the auto cycle few times without any objects inside the chamber, and by doing this you don't see any more brown residues, then it means the object will need stronger detergent or more rinses before sterilizing.