bonneville 1998 ?purchase - how to tell if manifold okay?

I have read horror stories about plastic manifold failures in bonnevilles and other GM engines. Found a really good deal on a '98 but need to know how to check for a healty manifold or if it has been replaced already, no records included with sale. Any way to tell if it is in danger of failing or if it has already been replace. Also, has the replacement part resolved these issues, or is it just setting the clock back to zero until the next failure. I would really appreciate an answer as I have to make a move my old car crumbles beneath me as I write this.