Most 2015 C‑Class diesels use Mercedes’ 4‑cylinder turbodiesel with the 7G‑Tronic automatic gearbox; both are common and parts/support are widely available in Ireland but genuine servicing is pricier than mainstream brands. Watch for diesel‑system items (DPF/EGR and, on some BlueTEC cars, AdBlue) and confirm the gearbox has had scheduled fluid/servicing — neglected autos can show costly faults later. The dealer’s “coupe” label is often wrong on listings for C‑Class saloons/estates, so check body style carefully.

• DPF and EGR behaviour: any persistent warning lights, recent forced regenerations, or heavy soot on exhaust during a test drive (short-town use causes issues)
• Automatic gearbox operation and service history: look for smooth, timely shifts, no jerking or slipping, and evidence of regular fluid/filter service
• Turbo health: check for blue/black smoke under acceleration and listen for unusual whistle/grinding noises indicating bearing wear
• Front suspension and steering: test for knocks, uneven tyre wear, worn drop links/anti‑roll bar bushes and any play in the steering rack
• Corrosion under car and around wheel arches/sills/boot seams — inspect the underside and rear suspension mounting points for age-related rust