The importance of scheduled carbon cleaning as maintenance on GDI vehicles

Hey all. First post here. Glad to virtually meet all of you and thank the people who have brought all of us together to make diag​.​net possible.

This client brought his car into us for a misfire concern. Client stated he had already replaced the plugs and coils. Plugs seemed to be correct and coils were of an unknown brand. During removal of plugs and coils to assess the clients work, multiple issues were found. None of the plugs were torqued to spec. A cylinder which showed a dead hole misfire, had a spark plug that looked to have been dropped and crushed the electrode. 

After replacing all plugs, coils and tightening all plugs to spec, quick test/quick cleared and test driven aggressively with no faults returning.

A month or so later, client complained about misfires again. After removing the plugs and checking the cylinder/valve condition with a borescope, it seemed the carbon build up on the intake valves had reached the point where the intake valves could not close completely. A compression test was run to assess the overall health of the engine and to confirm suspicions. Compression test numbers read …

We have owned the factory BMW tool for media blasting for quite some time and has proved itself time and time again. We have tried other brands and gravity fed media blasters without much success. 

Attached are pictures of pre and post blasting of intake valves and what the BMW factory tool looks like.

The compression numbers after media blasting were 205-210 across the board. 

I believe most people like to recommend carbon cleaning at every 50k but with all the stop and go here in NYC, every 30k might be a better option as preventative maintenance.

I have considered purchasing the ATS chemical induction cleaner after seeing it at the WorldPac expo. Has anyone had first hand experience with this system? Possibly running this cleaning yearly as a supplement to media blasting?

I'm sure I've missed some points here and appreciate any recommendations anyone might want to add.