I'm looking for this:
Mine sticks off, so I no longer use it, but I like the way it helps with engine braking so tend to use it in the mountains. I've already pulled it apart and fixed it once, lost one spring when it exploded (replaced), but it's pretty brittle and I think I had to glue it together last time I fixed it.
I've tried Rockauto, fordpart.com, numerous google searches and can't find it.
Even if I have a part number, it might be a start.
Last chance might be to go to a dealer and see if they can find it (or a wreckers yard).
Any idea what the part# might be, or where to find one?