Look for "heater core" or "heater matrix" as we call it over here and you'll find plenty of references. As for Barr's, I know of one US Saab enthusiast who used to be evangelical about it. Between he (a firm believer) and I (an engineer and sceptic), we did some investigation and established that there was no evidence to support his claims or those of the company itself (which was worrying - even their VP of marketing couldn't come up with any), nor any to back my fears. I still wouldn't use it, especially in a modern turbo engine. Confronted with a leaky heater matrix, I'd replace it and not have to worry about it again.
Was his name "Bob"?