De-carboned my 034 HFC , i was going to gut it by decided to try a good clean first. It was very sooty both sides of the core quite baked on aswell. Plan "A" block one end and the 02 sensor port, fill the cat with sodium bicarbonate powder and add some vinegar to start the reaction. Wow did that shift some soot etc, swapped round and did the other end and even more frothed out the top. Finished with a blast of cold water and now its having a nice gentle 100f dry out in the sun..lol will add a pic in a bit, but seems to have cleared a lot of soot from the cat and core.