Keep detailed records of all the repairs you did on your vehicle and ask the previous owners if they can provide you with their records.
If you need to have a mechanic diagnose a problem, show them your records. https://knox-todd.hubstack.net/questioning-what-to-do-when-your-motorcar-breaks-low-spirited-is-a-park-motif-for-many-repairs-arse-be-preferably-costly-and-wrong-moves-bottom-price-you-yet-sir-thomas-more-so-how-are-