Experience the same thing with Rapide. A year ago nagpatune up ako sa rapide, had no choice kasi sila lang open na shop ng sunday and i need to have my ride checked kasi byahe ako ng Monday morning. They used AC Delco spark plugs din. Wala naman naging problem until my next tune up. Nun nagpatune up na ko ulit this time with my suking mechanic, nun tinatangal na yun spark plugs nagtaka yun mechanic dahil pagpihit nya nun isang spark plug eh maluwag agad. Yun pala naghiwalay yun ceramic part ng spark plugs at yun metal thread. In short naiwan yun metal part na may thread na nakakabit pa. They removed the cylinder cover to access yun naiwan part pero di pa din maabot. So they recommend na ipamachine shop para matanggal. Pero nagtry pa din sila na dukutin using vise grip pero di makapasok ng todo yun vise grip. Good thing may pliers ako na medyo maliit yun body and it was able to get a grip on the remaining exposed metal part nun spark plugs at na unscrew. Na save ako from having it machined shop, the damage was slight scratches sa may spark plug hole then checked and removed yun mga metal shavings na naiwan from the spark plugs. Then ok na ulit ride ko. Di na ko bumalik sa rapide ulit and never will i use AC Delco again.