From my experience, repairing the springs may not be enough to level the seat. In my '82 I had one broken spring and I repaired it by inserting the ends into a vacuum hose segment which I wrapped in another, bigger hose which I secured with a hose clamp. As long as the two ends fit well and they don't separate, the vacuum hose will hold them. I also stuffed some carpet padding under the springs on the left side of the seat, but it still leans to the left! I think the problem is with the material that's on top of the seat right underneath the leather/MB tex. It's been compressed too much over the years by some fat ass.
What's the best way to get to it?