i went back and read all of what you said you did i dont know who was pointing you in the changes you did --- BUT a clogged injector can be the cause - if you have a hand held heat gun ( checker ) you can see what the exhaust manifold temps are between the cylinders a cold one or an extra hot one, will be a clogged injector ( or stuck one ) BUT i will say i had a miss in a 124 a few months ago and the distributor cap was cracked dont keep changing parts till you point out what is causing the issue

if you find an injector issue you can switch the injectors between cylinders and move the miss to another cylinder than knowing it is bad than you know for sure

old school method i was taught in the 1960s as a kid was to get a sheet of text book paper cut it into a 1/3 strip and place it accross a tail pipe of a car that runs correctly notice what happens to the paper ---- than place it accross the tail pipe of the car missing if you hold it against the side of the pipe and the motor is missing the paper will make a poping sound ( cant miss the sound it will be loud ) - than by that method you can start looking

with rubber gloves you can remove one spark wire at a time and look at the engine in the way it behaves the cylinder that is the cause will have the least affect on the motors idle or it almost has no affect when the wire is remover

CAUTION the live plug wire will bite you if your careless about holding it, think of it as a rattel snake, RUBBER gloves and rubber handle plires and pre remove the plug wires so they are just at the ends of the plugs and pop right off with no effort it will make it a lot easer to do it that way -- i still think its an injector after reading your post of course it is about the only thing left -- jz