Re-adjust the valves in about 1K miles, when they are far out-of-adjustment it may take 2-3 adjustments to get them to maintain a clearance.

Get it hot and run it hard, full throttle uphill and let it coast in gear downhill and repeat several times to work the rings back and forth in the piston grooves.

Do 2-3 short interval oil changes e.g., 1k miles on a hot engine, obviously be careful to avoid burns.

If concerned about carbon build up use a borescope to look down the intake runners OR remove, clean and re-gasket the intake. It isn't that difficult on a 240D. With the intake off you'll have clear access to the valve stem area.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer