Timing chain replacement

My friend is having major work done on his 1990 420SEL because he didn't change the timing chain. He said it should be done every 75,000 miles to avoid major work. Is this true? I just bought a 1990 300SEL with only 88,000 miles. I'm not sure if the timing chain was done. Should I have it replaced to avoid what my friend is going through? Thank you for any information.