I have seen many RGRA, or UGRA 90% efficiency furnaces with rusted/corroded inshot burners. They are ALWAYS on LP. I am helping a friend out that has the same problem, it lights the first 4 or 5 burners but doesn't make it all the way across to all 7 every time (105,000 BTU Furnace). The gas pressure is between 10-10.5" w.c. everything else on the furnace is within the correct operating specs. I was a service tech and have been out of the field for a few years and was wondering if Rheem has changed anything to correct the problem. If so what did they do?