10% HCl will speedily corrode most common metals which could be used in the water cannon construction. The worst affected will be the sealed bearings on power shaft. Getting HCl in the eyes is a recipe for being blinded, unless immediate attention is received. Also it would give a very serious respiratory damage. Sulfuric is no fun, either. Why not spray VX and be done with it?
Nitric would eat the metal, too.
So, speculating on what was in the tanks, maybe some dye, (rust in the water is possible, too) and something else, possibly an agricultural chemical pesticide/herbicide, although there would be a definite odor for either acids or ag chemicals.
Tough to say with Noriega, it could have been most anything. We do not have enough info to do much besides speculate.