You need to have your Home Inspector take a look at the house, the ENTIRE house. Get your OWN, ASHI-Approved Home Inspector. DON'T take a reference from a Realtor. Find your own, or talk to friends to see who they used. Just find someone that's ASHI-Approved.
Also, hire yourself a Real Estate Attorney. What you do is have the 'crack issue' added into the Agreement of Sale. You CAN'T do this verbally because the Agreement of Sale is the LEGAL document. Also, you have anything else you want put in the AOS, like Termite Inspection. You can figure out how much it will cost you IF you end up w/a problem w/the crack. It WILL cost more than hiring an Attorney and Home Inspector, combined! In short, if you're spending $100,000 for the home which over 30 years is about $300,000, you figure out if it's money-well-spent to hire the Attorney and Home Inspector. In MY mind, you'd be a sucker is you didn't do this. (Sorry, you brought it up.)
Do express your concerns to your Home Inspector and Attorney about the crack. If the HI isn't qualified to tell you about the crack, he'll probably ask that you hire a Structural Engineer. Maybe you can get the current Homeowner to give you the paperwork for the 'fix'. This will help the Inspector determine what it was they were actually trying to fix. If they don't have it, suggest they contact the Contractor. If he's out-of-business, or you get an 'excuse', DEFINITELY have an Engineer look at it. Maybe your Attorney can get the Homeowners to PAY for it. Ask him/her! They'll tell ya.
Just because you can't see any 'damage' occurring doesn't mean all is well. My best to ya and hope this helps.