Is acid treatment recommended only for engines with raw-water cooling, or also for engines with heat exchangers?
I didn't mean to imply that it's a recommended approach. To the contrary, I've never heard a diesel marine mechanic who's opinion I respect recommend muriatic acid treatment. One major reason is that there is no definitive interval before which acid MAY affect seals and rubber parts while still doing anything effectve to break up caked material which is not porous enough to allow penetration of acid beyond it's surface layer. What I suggested is that If someone wanted to try it and was concerned about the acidic effect of parts, dilute it slightly but that only minimizes the efficacy of the acid making the process that much more futile.
The only was to KNOW is to remove the suspect part(s) as the original poster implied he did and inspect the cleaning process result. Using vinegar which is about as acidic as soda pop is a feel-good approach only.