I think I got lucky with one of mine recently. I was planning on changing it based on the 8 year lifespan- I think it was the original from 1992. When I drained it, I noticed some kind of oil in the coolant. Turned out to be tranny fluid. Flushed the tranny and everything seems good. So I'm heeding the advice about lifespan on our other cars and am changing them out in our fleet of three.

FYI- new Nissens are only about $150 from a variety of sources: Amazon, FCP, etc. Not sure what you will pay for one at the PNP and getting it checked, but unless dollars were really tight, I would go new unless I found a used one that looked really new. Otherwise, I would expect that most are at or over the 8 years.

Lyle