I have a Jotul Oslow and I have been getting a significant amount of creo on the lower ash pan door. I'm burning 18 month SSS Cherry Maple and Pine, with no hissing or smoke once settled down. The gaskets are all in good shape no leaks and I burn regulary at the 500- 600 mark. This creo looks like black spray foam and is dry and crunchy. My stack gets cleaned once in the spring and has just powder. Window stays perfectly clean just a little dust to clean one a month. Any ideas? Not really a problem just wondering if anyone else has the same issue.