Man, that's rough. I learned the hard way too with some old radio parts. Now I just hunt down the original-spec stuff, even if it takes forever. Saves so much headache in the long run.
My buddy put diesel in his old Honda once, just a complete brain fade at the pump. That engine was never right again, just a total loss. He had to sell it for scrap a month later. Sometimes a single mistake really does wreck things forever. The look on his face when it first choked out... he still gets quiet if you bring it up.