Obviously, your inspector is aiming to cover both your butts, while the other inspector has an incentive to help sell the house- that's a strike against the sellers' inspector. Moreover, think about when you need to sell the house. Do you want to tell the next buyer it's fine? When can afford to replace it? Chances are, it will need to be replaced eventually... it looks like it's ticking to me.
But since you are asking, you must be doubting your own inspectors' experience or intelligence. Caution is also age related; older people tend to be more cautious, and wiser. Bear that in mind, it's only a tendency. So, do some people work... find out about them. And try to get another opinion from someone who can be there to physically inspect it. Maybe you could get two new inspectors. If they don't agree, then expect to replace the pipe since the owner will not.
Rationally, both inspectors work for themselves of course and have their reputations. Check with BBB and/or Yelp and/or Angie's list, and/or Facebook and/or ask them for references and figure out which guy has the reputation. Pay attention who their clientele is. If the sellers' inspector's clientele is primarily people selling houses, this would make me less apt to believe what he's selling.