Twice in my life I've 'fixed' vehicles whose owner(s) told me a mechanic said the engines were 'toast' by simply doing a modern tune up with OE parts. A modern tune up (to me) is installing a new air filter, spark plugs & coil(s). One was a 20+ year old pickup & the other was an early 2000's Volvo with the turbo 5 cylinder. Similar to your tale the Volvo had previously had no-name Chinese coils installed which the owner said only made the car run worse.