Most 2018 Astras with diesel engines are the 1.6 CDTI family — economical on the motorway but fitted with DPF and EGR systems that dislike lots of short urban trips. Being a manual, clutch wear and the gearbox synchros are the usual mechanical wear points on an 8‑year‑old car; replacement is straightforward but can be an intermittent cost. Check whether the car has had occasional longer runs to allow proper DPF regeneration and a record of injector/turbo attention if mileage is high.

• DPF behaviour — look for frequent forced regenerations, warning lights or heavy soot/black smoke after hard acceleration
• EGR valve and inlet carbon build-up — rough idle, poor response or loss of performance under load
• Clutch for slip, judder or unusual noises and signs of a wearing dual‑mass flywheel (hesitation when biting off)
• Gearbox engagement and synchro feel across gears (especially 1st–3rd) for crunching or scraping
• Underbody and rear-arch corrosion, and condition of front suspension bushes on an 8‑year-old car