Well if all your other manifold bolts came out and you got that much of that one out I would say you did very well! IF the engine was out of the car you would be able to drill out the rest of that bolt, or use an extractor etc. But with it in the car you got no shot. Just no room to work. You might be able to get by with putting all new bolts back in and just using a shorter bolt in that spot? Clean up the threads first. I'll bet it tightens pretty well. You got some threads to work with.

And glad the ramp held up for you! For what it's worth my rear main leaks too. Sometimes more,sometimes less. I keep trying to convince my wife we need to have the engine rebuilt so it "will stop leaking".