Hello Gene. I have read about this cleaning elsewhere on the forum posts so I checked it out in my Repair and Maintenance manual. Here is what it says:
The flue, which is located directly above the burner flame, should be cleaned periodically to remove rust, scale and soot. How often this is done is determined by frequency of use, quality of propane and region of country.
After removal of the flue tube, the spiral baffle inside the tube must be carefully removed. Than a shotgun bore brush or a special brush available from the refrigerator manufacture is used to clean the tube.
I read on some of the other post on here that people had to remove their units from the RV to do this , so looking at my situation ( and possibly yours too ) I saw an easier way to do this without removing the unit. I don’t think that the problem comes from burning the propane I think that it is the type of metal used in the manufacturing of the stack that is causing the problem due to flaking. If I ever have to remove my unit for any reason I am going to have a replacement stack made of Stainless before I re-install it.