I've been using copious amounts of ACF50 on mine, and although much of it probably burns off, it's yet to go rusty. On my Kwak turbo, the turbo unit looked like solid rust. Not really a problem, as it was a thick casing (it needed to be, as a turbo impeller spinning at something in the region of 200,000rpm would be proper lethal if it failed), but looked unsightly. Unfortunately, I can't remember the name of the stuff I painted it with (it was 30 years ago after all), but if they still do it, it'd be perfect for the job. Maybe someone will know it by the description: A thin, milky white liquid with a slight purplish tinge. Painted it directly onto the rusty turbo casing, and when dry it went a very dark bluish-purple, almost black, with a slightly glossy finish, and was as hard as rock. I think it was a rust neutraliser, as well as covering up the unsightliness. That's what I'd use. A turbocharger gets much hotter than a normal exhaust - glows bright red, and this treatment survived that extreme for many thousands of miles. Sure I just got it in a local car parts and accessories retailer at the time too.