To clear the ring I use a wallpaper stripper/ steamer. I plug it in the manifold, let he car iddle for a wee while, then rev a bit, then iddle again.
To be honest I am not sure if it work but I do it as a maintenance as I am pretty confident it do some cleaning. The steam is coming out the exhaust.
The idea of the wallpaper was from a member of the veg site, I think it good. Take a wee while tho to go through 5 litre of water.
Or as posted above, the H2O injection is the best.

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E300TD year 2000. RUSTY SOLD
cost a fortune to maintain on the road
but run well on WVO
Second Merc died due to corrosion ( NOT rust) How can mercedes get away with that for so long?
Third lasted a month then went away...
Fourth now... Corroded too...