So how are these cars decarbonized?

What about the products called engine flushes? The ones you pour into the engine right before an oil change, without driving?

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'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)