I gave my M55 cast fs a good cleaning today. When I got to the part where you open the two round ports on either side of the burn pot I noticed the whole plate lifted up. I was able to remove the plate completely.This allowed me to clean much better and also I was able to shove the vac hose into the exhaust shaft that pulls the exhaust through the combustion blower. Never would be able to clean this thoroughly by just opening the round ports and vacuuming them. Dont know why this method isnt in the manual. Give it a try if you havent already done so.