I would ask the plumber how long he thinks they will last and budget accordingly to replace it. Tell the seller that it’s a concern to you and try to negotiate as much of the replacement cost out of the purchase price of the park. Educate the seller on what it is, why it was used and that it will eventually fail.
Do you have a recording of the camera work? If so, and if it looks bad, show it to the seller. Bad orangeburg will be bowed or crushed… I know because I have it at my house and just had it snaked yesterday due to root intrusion… I’ll be digging it out next month