Another dumb one, sorry. I have a new high level exhaust. At some stage, a previous owner fitted a new stainless steel pipe and end can, and where the stainless pipe meets the mild steel collector just under the swing arm, it has seized solid. I've heated it (not too much, as it's very close to the rear tyre). I've beaten it with hammers (large and small). I've tried to drive it off with a big screwdriver from the left side of the bike. Nothing seems to be shifting it.
Now, I know I can take the old pipe off with an angle grinder but I'd rather keep it intact if I can. Any clues?