[30 Tudor]

Not only bad with cast, but high carbon alloy steels are subject to hydrogen embittlement. Which can be caused by any acid, but HCL is the harshest.
The hydrogen can work its was in to the molecular structure of the steel and combine with it and form a gas that will build up enough pressure to break hardened steel.

The plating industry is very cautious of this problem. It doesn't hurt to study it out a bit.
A materials/metallurgist friend of mine in the nuclear industry assured me that a quick wash to clean wouldn't do any damage.(I am referring to hardened steel, not cast)

I am pretty anal, I would run water with baking soda for a while in the engine
if it had any Hcl put in it, just to be sure, then flush with phosphoric if nervous about rust.