Ring soak is useless and a waste of time. Nothing will dissolve carbon, if that was your intention. You need to physically scrape carbon off so it is like an engine overhaul. However, if it makes you feel better then go ahead. It ain't going to do any harm nor good.

Do a compression test and it may give you a clue on the health of the cylinders.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.