Old 02 sensor, best gas milage?

[Myke456@aol.com]

I've been driving my 87 5kcsTQ, since new, approaching 200k miles. The 02
sensor has never been changed! Previous cars had lights that stayed on until
replaced. Since this model has no light, I thought perhaps there was no 02
sensor. Since participating in this group, I've found that I do indeed have
one, and its way overdue for replacing. But...I can't help but wonder...since
the engine runs great, should I:
1) Wait until it "goes"?
2) Any ill effects from running "old sensor", if all seems well?
3) Could this old sensor be the reason why my mpg has increased since 100k,
from average of 19 to 27mpg? (same driving style, actual miles, not computer)

Thanks,
Mike Aiello