I seem to have a slightly different wrinkle on the starting problem.

When I turn the ignition on, I have a very short window during which the engine can catch. I always hear actual ignition, but if I release the key too soon, or crank too long, the car will not start. This time frame is less than 2 seconds. If the engine doesn't catch, I can forget about starting for an hour or two. If the engine starts, it runs like a swiss watch.

The problem used to be intermittent, but is getting more frequent now. Seems to be worse when the weather is hot.

Any ideas?

I had a similar problem with my 87 300E. It would crank over and I would hear it try to catch but it wouldn't. New wires, rotor, cap & coil. Even though it was new, the coil was intermittent. The tech caught it so I can't say how to check it but it may help.