Classic/Antique Car Repair: M-B OM617 engine performance

Question
I own a 1984 Mercedes 300SD turbodiesel. Has anybody had success making significant power gains with the OM617 5-cylinder engine? The forums I read (and they might be part of the problem) display lots of blood, sweat, and tears for a 15% net gain. Call me naive or stubborn, but I believe everyone who tries isn't using the most intelligent and meticulous approach.

Answer
We have three 300D series cars. They have well over 200,000 each.  82, 83, and an 84. I have needless to tinkered a fair amount with them. Each time I have reverted to the way it came from the factory. The most critical thing that I have found is the valve adjustment . It requires special tools and I would suggest a trained Mercedes mechanic.these engines were designed to meet us emmision, give excellent fuel economy and run forever pulling a heavy car down the road at 80 plus miles per hour while delivering 25 to 30 miles per gallon. Two of our care are in show room condition and one is in good used car condition.