Thanks to everyone for their respones. On the O2 sensor, before I got into all of this I had put a new one in there, and to verify operation, swapped with the new and old (because the new one was a more recent Bosch revision).

Yesterday after my post, I went all over the car again looking for new vacuum leaks. I at last asked myself the dumb question-- did mechanic #1 put the fuel distributor on properly. That is, was it sealed properly? If I had 1 ounce of real experience and common sense on this, I would have asked myself that question immediately. Anyway, at last I asked it.

There is s an o-ring you place onto the bottom of the fuel distributor where it connects to the air housing. This o-ring MUST BE LUBRICATED before installation and needs to be carefully handled during installation of the fuel distributor. The distributor cannot be twisted around once put on the air housing.

So, first I leaned the car-out by adjusting the CO air/fuel mixture screw (the 3mm allen adjustment in the air sensor housing) so that the car would miss at idle. I sprayed some carborator cleaner in that seam (gap) between the fuel distributor the air flow housing. The car immediately stopped missing and then started again. I did this many times consistently. This confirmed a likely issue with the fuel distributor seal. I called mechanic #1 and told him what I did. To his credit, he agreed that he'd pull the distributor out in the morning (this was yesterday evening that I spoke with him) with me right there and we'd inspect the seal. One thing I will say for mechanic #1-- he is customer focused and very friendly. He has re-earned my respect. At any rate, he pulled-it out and I learned a few things while he did it and he showed me a few things. Note he did not install the fuel distributor, one of his other mechanics did. The seal was, without question, torn-up when he removed it. He acknowledged that. We also both agreed there is probably also a manifold leak. But we also agreed this fuel distributor seal was a big issue. I handed him a new gasket (I picked it up from MB yesterday) and he carefully installed it as I watched. He put it back-on. I took the car for a drive and it has massively improved gas economy. I did not test the CO rating while driving (on rollers, that would have required another run by the emissions station) and I have verified that the IDLE CO rating on these cars bears no relevance to the actual emissions rating because in my state they test with the car on rollers. I looked at graphs from my last emissions test results (run in a special test mode at the station) and the driving CO value is 1/5th of the idle value (the tests at various speeds). So for example if you are blowing 4% at idle, that has nothing to do with what you blow at 15 mph or 30 mph. In fact, my experience says you can divide by as much as 5. The car, already smooth, was now driving to an even better level (I didn't think it was possible) and the gas economy is now ** dramatically ** improved. I went for 80 miles gunning the engine whenever I could and the car used a fraction of the gas it used before. This improved gas mileage tells me that far less unburned fuel is now going out the exhaust while driving and hence the emissions are greatly improved. I will have it tested again at some point to verify, but the car is now different and I believe the issue can be put to rest. I will say that this new fuel distributor and the unclogged catalytic converter gave the car about 50% more power than I ever experienced owning it. Even if I lean-out the car at idle so that it misses at idle, its acceleration and driving is miss-free and clean. Only one final possibility remains with this car in my mind, which is that with its new power (unclogged cat and new properly tuned fuel distributor), it may now be more sensitive to any manifold leaks that may have existed before it. I will determine that during testing in the future and will share results. But again keep in-mind that prior to this fuel distributor/injector/cat work a few weeks ago, this car sailed through emissions for the past 10 years and only recently passed on everything except for NOX and there I failed only at one speed (15 mph) and only because they had made the NOX requirements more stringent than in previous years-- I also only failed by about 10% over the max allowable. All other numbers including CO were/always have been much lower than state requirements.

I've learned a ton working on all of this and have made nearly every mistake you can make but learning-- I learned by reading posts/reading manuals/watching and managing mechanics/working on it myself and owning this car for over 10 years now. I hope I have the energy and stamina to sum-up my recent experiences hoping they will be happy for others. Again, thanks to everyone for their help,.