Scaredy is the septic tank clogged or the leach field? Septic tanks are super simple,as you probably know by now. What is hard about unclogging it? Cracked badly and deteriorating is a problem.
I’d be more worried about the leach field area. I would not buy a property that didn’t have plenty of good area to start from scratch if there was any doubt.
Also,if you have not, you want to be sure that the Health dept. is going to allow you to pull permits for whatever worst case scenario a knowlegeable person anticipates.
I wouldn’t close until I had permits and a site inspection completed. if required.