[Arran]

Joseph;
I don't think that it makes much difference when it comes to thick, crusty rust, it's going to take more then one application of either a wad soaked in vinegar, citric acid, or Navel Jelly to get it all off. I once had a chassis so bad that I resorted to using muriatic acid (HCl) on the rust, it worked somewhat faster but not better then vinegar, then there are the fumes, in the end I stripped all of the parts off the top of the chassis, drilled out the tube sockets, (I did not remove them, just pushed them down) and took a wire wheel to it with an angle grinder.
Regards
Arran