Steam Cleaner recommendations

[used red MN]

Never heard of that. How does it work? Do they grind it up or something?

I have seen it used at a refinery during maintenance events where vacuuming all the sand from sand blasting the same area would have added to much time. The blast machine is capable of creating the pelleted dry ice from liquid CO2.
Video of example unit

 

[Fritz Maurer]

Kind of expensive and hard to get, but Zep made this stuff called Zep-Alume..... made for dissolving soot from the sides of semi trailers.

I tried some on a D4H motor with a leaky muffler, and it took off the soot and much of the hardened grease around the cylinder head. Some of the paint that hadn't seen daylight for years looked brand new.

But you'll have to decide if the amount of dirt you have to remove is worth buying the stuff, or just using elbow grease , which costs nothing.