* These days I primarily work on the 10-30 yr old MBs, with a car newer than 10 yr old in here and there. Decarbonizing an intake manifold and cyl head ports on the older cars, safely and inexpensively using the "wonders of chemistry", is always a popular topic.
* I recall, from 5 years ago or so, a 944 (Porsche) customer who had had a "decarbonizing" service done at a high-volume, quick-tune shop and now had a noise that sounded like piston slap. I pulled the cylinder head and indeed found the cylinders scored. After pulling and disassembling the engine, I found the piston skirts to be scored even worse. That turned out to be an expensive, not-so-quick-tune. Unfortunately I never learned the brand name of the decarbonizing agent. The customer said he watched while the cleaner was fed to the running engine through a vac supply port. The decarbonizing agent very likely was the popular Sea Foam; however there are probably several other decarbonizing agents on the market that are delivered the same way.
* That experience convinced me that the direct-feed decarbonizing could create much more trouble than it solved. Of course Porsche has used different metalurgy in their cylinders and pistons (e.g. Nikasil coatings), so that may have just been the perfect storm scenario. At any rate, direct-feeding a decarbonizing agent shouldn't be just a weekend recreational activity. It should only follow a thorough search for any other performance-robbing maintenance issue. Hence I only add decarbonizing agents to the tank, and Sea Foam is my favorite since it's also a fuel stabilizer (for storage).
* I've read the Sea Foam search threads and watched a number of Sea Foam videos on YouTube, but nothing has convinced me to risk a direct-feed. I'd like to read some pertinent before-after testimonials.
* By the way, the only additive that is, as far as I know, FAA approved (and they don't approve anything easily), is Z-Max. It's the only preventive-maintenance additive (package) I use (not direct-feed) once a year in my own car ('90 300CE 24v).