It shouldn't suffer with age, because the car is in near mint condision 78000 orginial miles. So age is not its problem. I am thinking it is something mechanical. I have ac delco plugs, and they can't be fouled because the engine runs fine when I did the above. So it may very well be the bosch 02 sensor. Hell, I don't think they are designed to last 6 months but 1000 miles. But would it be worth it to buy an ac delco O2 sensor as they are about $60-70 dollars vs. $20 for the bosch? But as I once heard "you get what you pay for."