i am putting the landlord in the wall o shame. i found four cracks like this one between two luxaire's in a rental house. landlord said i was trying to "f*** him over" & "its not that bad, give me a break". he also said i should put some furnace cement on it and it will be ok until next season. i should have known not to go there when he called and said he needs a rental inspection but " theres nothing wrong with them, i know because i used to sell furnaces". oh yeah he was almost 90 yrs old and the furnaces where installed in 1978.