Yes, I wire wheeled inside and out, then sprayed a bit of phosphoric acid up in there to address the rust; then rinse that out and wipe it all clean with acetone prior to applying the 8875-Thin. The Thin is very thick and sticks well. Used rubber gloves to spread it around the inside of the upper pipe and put a thick coat on the lower.Yeah I am not a welder, but I assume expansion and contraction is the point of the slip joint. That is why @IDIoit uses a bellowed section. I just have talked with the guys at CDD to see if they had a product to fix this problematic joint and they said they have just welded them up in the past without issue.
Hopefully this Deacon stuff works well. did you have to clean the joint real well?
I also had a minor leak on my passenger side manifold:
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