It was a 1990 735iL. It was in pretty rough shape unfortunately and I didn't have the $$ to bring it back. I did make it better than when I got it though.

I found a brand new BMW OEM differential to replace the blown one it had. Had the fuel tank fully resealed, cleaned up some wiring, etc. But the AC system was completely missing and the body work was pretty rough.

Someone else ended up buying it from me and planned to take care of it so I'm hopeful it still drives!

It was a fast diesel, in 1993. For today's standards both the 525td as well as the 525i would not be very impressive. The latter more than the former though. But the handling characteristics, driver communication and joy to drive were great back then and are still amazing today. The 525td had one of the smoothest diesel engines I have ever experienced. From the sound to the power delivery it is all a gradual and consistently predictive curve.

That 300td is a W123 with a 5 cylinder engine, right? We have a 240d, they don't easily rev up but they don't stall easily either. In their day, these were very respectable in terms of diesel car performance. They're very reliable work horses and generally nice to drive, though there's a very very big gap with the driving dynamics of the e34.

My main concern with the diesel is not as much the price as it is the impact on the environment. They're made for pleasure or the occasional freight hauling at this point. Keeping that in mind, the 240d (and thus also the 300td) are very accepting to alternative oil-like fuels, like biodiesel or really anything you can get your hands on. We used sunflower oil at some point. Make sure there's sufficient regular diesel for starting the engine. With how they behaved in their day, I doubt they'll pollute more with sunflower oil too.