The factory fitted plugs in my 250 were changed at the 6 year mark ( 2013) when the car had done 22,337 miles!, according to the schedule they should have been done again in 2019, but with only 42,000 miles on the clock then, I opted not to as the plugs had only done 20,000 miles! The car has less than 45,000 miles on it right now so I don’t even think they will be getting done in 2025! I will prob wait til they start to play up or when they have done 60,000, which will be at the 82,000 mile mark!!! Could be some time.....