can-zone

About a year ago my car's service light went on. I'm very nervous about that kind of thing, so brought it in right away. Turned out that the OG catalytic converter was toast. Got a new one installed by my regular mechanic. Who is great. But the new one was making some crazy sounds. So brought it back. Sounds gone. Weeks later, light is on. I went back in, mechanic said something was wrong with the sensor. Or some such. Fixed it. Same thing a few weeks later. Since then I've rinsed and repeated this 6 times. I don't even remember what year it is anymore. My mechanic isn't charging me for these visits. But every time I drop it off he has it for 3 to 5 days. And I live in New York so it's a pain to deal with. Most recently, the light turned back on and he said, throw some "Guaranteed to Pass" in the engine and go through a whole tank of gas and then to come back. He also said the car will drive fine, it's an emissions issue.

While I'm sure he's right about all of that, I never know if the engine light is going off for the emissions issue or another issue altogether. I've had a few scary engine things happen with this car (it is 23 years old), so I'm always on the lookout to changes in the car's performance.

I'm kicking myself for not keeping better records. I've only got two mechanics I've ever worked with so I imagine I can pull their records from receipts or something.

Any ideas or recommendations to ease the pain here a little?