Dave, I can understand your concern and desire for a safe your son. My father must have had the same thoughts when he gave me my first car, the 1981 300D. I believe this is the same chassis (123) that you are interested in for its safety. Let me recount some of my experiences in the car.
First of all, the car was slow. Almost too slow. I suspect that you want to get your son a slow car so that he is not out drag racing. A diesel is good for that safely, but too little power can also be a hazzard when pulling into traffic. I have also driven the same chassis 240D which in my opinion is so slow that it is a hazzard.
As far as crash safety goes, it can be described in one word: Panzer. This thing is a tank. I was in two decent wrecks with my 300D and it came through both times.
In the first wreck, I was hit from the side by a full-size bronco. This in the right quarter panel. The drunk ran a stop sign and nailed me as I went through the intersection. I saw him coming at me and gave it a little more gas to try to avoid the collision. A slower car would have put the collision into the passenger compartment. The only panel damaged was the quarter panel.
The second accident could have been alot more serious. In a freakish accident, a box fell off a truck ahead of me in rush hour traffic on a six-lane highway (US19 in clearwater,Florida). I swerved, and the sidewall of the tire collapsed, sending me spinning as though I had a blowout during a sharp turn. What started as a swerve to the right progresed into a skid across all the lanes to the left lane, leaving me facing oncoming traffic while still travelling in the correct direction. At this time a (then) new 1990 Honda Accord(ion) smashed into me head on and sent me spinning (again) across traffic onto the right shoulder. I thought I was going to die, but I escaped unharmed (minor bruise) as did the people in the Honda. The Honda, however was totalled. It had dived under the front bumper of the 300D and bent the bumper upwards, punctured the radiator, and pushed the driver's fender slightly toward the driver's door (closing the gap). This was about 2 grand in repairs and it was back on the road. I have seen the same car type in similar accidents, and it always hold up well.
I retorspect I am not sure if the car (300d) was really too slow, but I do believe that a 240 does not have the acceleration to get out of harm's way. I do often recommend the 123 chassis mercedes, but usually the 300D Turbo, because it has a good balance of power and economy as well as safety. Those cars are no slouches, but they are no dragsters either. Just keep in mind that acceleration can be a safety feature.
Sorry if a babbled on a bit, but I have many fond memories of that car. Here is a little more babbling:
The car finally met its fate by my brother's hand (as do most cars he drives) when he was driving (without a license) slowly in the right lane of a highway when a van travelling at high speed had rear ended him, destroying the trunk section and evrything he had in it (some newly acquired computers from the tech show he had attended). It was a complete loss, as he was not legal to be driving and the insurance would not pay. He was later given my deceased father's car (killed at the same intersection as my Bronco accident while driving a Toyota Previa which was also too slow to get out of its own way). My brother then wrecked the car and gave it to me with some poor repairs. That car is now my daily driver, the '93 300D. I have the car mostly back into spec from the accident, but it still has some very minor tinkering to be done beore it is finished.
I hope that some of this helps you, and thanks for the trip down memory lane.
PS, It was also very economical and reliable, only leaving me stranded when the water pump blew. I think in the 123 chassis, newer is better.
\'87 Mer-B 300D (220,000 miles) (sold)
\'93 Mer-B 300D (173,000 miles) (sold)
\'87 Porsche 928 (101,000 miles)
\'98 Dodge Ram quad-cab (250,000 miles)
\'2001 CLK430 Cabrio (50,000 miles)
Past cars: 1969 mercedes 250, 1981 300D, 1972 220D