I've read that Mercedes has parts available for all the cars they have built since the second world war. Are there any other auto manufacturers who keep parts for vehicles that are decades old?

I doubt they really "carry" parts. Carrying inventory is bad for business. I do see they offer authentic MB parts for cars back into 70s so they may still produce parts in batches. I know Porsche has all the drawings and specifications for parts for their cars going back into the 40s. And, with additive manufacturing, can offer rare parts for a cost. Maybe Feets can answer the MB parts situation for sure. But I am guessing they don't have a warehouse full of every maintenance part you may need going that far back. As for domestics, who knows, but I am sure its only the minimum they have to comply with the law.

john deere has been good about parts for a our 1968 350 loader and our 1985 2550. We could also get parts after I wrecked our 1973 24T baler
Thats all I got

Old? My wife has a 2012 Chevy Sonic. Nice little car. Not well supported in the aftermarket and the amount of stuff for that car that is discontinued from GM is becoming an issue as this thing ages and needs stuff fixed.

I'll stick with vehicles that are common as dirt for my daily drivers.

Mercedes might have the parts available but you pay out the wazoo for them. Once they hit the typical age where support drops for other cars most of those Mercedes parts they make forever is stocked in Germany with prices several times what they'd normally be and long lead times.

Mercedes stocks relatively few parts for older cars. In fact, they sold off most of the inventory of SLR stuff to Vintage Parts several years ago.

When it comes to the classics, Mercedes does have Classic Centers in NJ and CA. Those shops are pretty small but they can either locate parts for vintage Mercs or arrange manufacture. In fact, if there's a vintage MB you're interested in buying they can either help locate or restore the car you want.

Make no mistake. You will pay dearly for those components.

Want a new white steering wheel for a 1963 230 SL it's not a problem.
If you're looking for something like a vacuum pump on a 1983 300SDL you're out of luck.

On an episode of Jay Leno's Garage, he was talking about his Gullwing 300SL and he said that while Mercedes might not stock the part, they have the original blueprint and can manufacture you any part you need for your classic Mercedes. I think he needed something silly like the fuel injection intake plenum and that set him back $7000.

Hyundai has a program like that. I needed an upper sump a few years back and they had none in stock. I placed my order and 9 weeks later, they shipped me a brand new (stamped the previous month!). It was only $700.

When the dealership thought I needed a new trans, same deal. Hyundai would manufacture a new one to the tune of $8000 Cdn. Lucky me, I found an NOS one sitting in a transmission shop in California. The owner was happy to get $1200 US for it. Joke was on me though, it was a clutch failure.

Thanks for the reply Feets. It is strange that Mercedes provides parts for vintage models, but skips over the cars that are a few decades old. Would I be correct in guessing their decision is driven by money?. Some of those vintage Mercedes bring HUGE bucks. The owners of such cars are probably willing to pay the big prices for parts.

What is the upper sump that RamblerMan mentioned?