One of the e34 touring's party tricks was it's unique double sunroof. Open the front, or open the rear, or open both, overlapping in the middle. I had a 525 touring back in the mid/late 90's, and my kids loved this. It was great for ventilation, and eventually, the front section jammed shut. At least it didn't leak, and i still used the rear sunroof for great, draft free ventilation.
One handy thing, is there are plenty of parts cars out there. I found a fully functioning sunroof assembly from a late '95 525 touring. My thinking was to find the newest that i could, maybe there were some updates along the way that would make it better. The seller was/is a friend of mine, and he guaranteed that it worked, and helped me remove it from his parts car. As you can see in the intro pic, the entire double sunroof assembly easily fits in the back of the wagon. It's surprisingly light, with its plastic framing. It is held in to the body with a couple of clips, and a million nuts. Note this isn't really a how to/diy. I did this over 2 years ago, so just pulling some pics off my laptop, which are incomplete on many of the details.
Obviously, my parts car was white, but when installed and plugged in, everything worked. The panels are easily removable, so once i was sure everything functioned, i swapped my original body panels onto the new assembly. The panels do make the assembly a little heavier, but without them, the structure is really flexible and hard to handle. I was worried i'd break the plastic frame without them. Besides, i had my sons to hold the sunroof up while i started bolting in the hardware.
There are some "while you're in there" parts that make sense with this project. The headliner has to come out, so perfect time to recover it. When the headliner is out, you can easily remove the roof rack rails, if they need refinishing. I pulled them so i could wet sand and polish out the roof . (trying to get some more life out of some older paint). You can see in the pics below, it really did polish out nicely.
I worked at a detail shop when i was in college, so i still put those skills to use, though modern products are amazingly better than what existed in the late 80's- early 90's. Coincidentally, one of our shop accounts was the local BMW dealership, which is what started my love with the e34.
The sunroof is a pretty straightforward remove and install. I did it on a Sunday afternoon. While waiting for the headliner panels to get recovered, i sanded and polished out the paint. Another few hours work. Touring headliners are pretty easy, just a big jigsaw puzzle. Nice result. Yes, i am in the camp of 'use your sunroof' but keep the rails clean and lubed, and the drains clear.