Hello, I have had this problem as well in the past. I did not think much of the suggestion of pounding the brake rotors since they are so thin to begin with and not being vented like a conventional rotor, lacked structure to pound on with a sledge hammer without the risk of distorting it somehow.

I worried about bending it, so I decided that once the caliper is off to take the caliper bolt and thread it back in with the caliper off. This will give the extra travel for the bolt to go through and physically make contact with the rotor. With the caliper on... the bolt bottoms out on the caliper with the bolt head and won't reach the rotor, obviously.

I suppose you could put something soft between the tip of the bolt and the rotor so as to not marr the surface or a thin piece of plate to spread the force out.... I did not and had no problem in that regard, but you could if you want.

Tighten the bolt a WEE bit at a time. do one side and loosen the bolt off and rotate the rotor 180 deg. then tighten it again a small amount. Do this equally around the rotor and it should "pop off".

I have used this method on two of my w123 cars and it did not seem to harm the rotor at all. The 79 for sure had the rotors from factory and I am almost certain they had never been removed until I got it. The 80 wagon rotors pretty much slid right off. I think the p.o put new rotors on some time before I got it but were on there tight enough to use this method. Both rotors were reused without resurfacing and give no vibrations from either car.

Take your time and be aware that when it comes off it sounds like a gun fired off in front of you. (the 79). I did the 79 first and perhaps was not as diligent in applying even pressure around the rotor and maybe that is why it sounded so loud.....as if loaded up more on one side.
Maybe in hindsight you could use a ratchet and count the "clicks" as you tighten so as to press it off evenly. I would say to just tighten a couple clicks at a time to reduce chances of bending the rotor. It takes hardly any force. The trick is applying small force evenly. The caliper bolts faired just fine and also were reused with no problems.

I used no oil or heat for either car but did have a wire brush on the end of a drill to clean the rusty mating surface as best I could around the hub/rotor junction. Maybe a little oil would make it even easier and might not be as loud.

Hopefully this is an acceptable method..... In my opinion much better than the sledge hammer approach on your brake and hub parts. and requires no special tools other than what is on the car and of course a wrench/socket to turn the caliper bolt. I imagine the key is to apply even pressure around the circumference of the rotor.

One more point I would like to add is that I really did not tighten the bolt much at all before unscrewing and moving the rotor to apply even force to the other side of the rotor. You could even use the lug holes as a reference and use a criss cross pattern to press it off much like tightening the lug bolt on your wheel when changing.

No sweat involved and the rotors were off in under five minutes. I was glad I stopped to think this one through because at first I was really not sure how I would get them off. The 79's were so bad that even after wire brushing.... the rotors looked like they were in one piece with the hub. I live where it is cold and slippery for much of the year and we have alot of salty roadways in the winter.
I thought maybe this could help out others that encounter this and was suprised that it was not offered here as a tip or trick. I am sure I was not the first one to use this method, but I would prefer it to hammering on my hubs and rotors with a sledge hammer which is all I found when searching. I meant to type this out years ago but forgot. I was just checking this diesel section today and saw the topic, so there it is guys.... the press and the means of removal is included on the car.