My 40k mile Vauxhall Meriva has just been serviced by the main dealer who, without asking, added some substance to the petrol and engine oil and called it an ‘Emissions Service’ then stuck £20 on my bill. They claim it will remove sludge from the cylinder head and camshaft. Since anyone who looked in the filler cap could see that the engine top end was perfectly clean and I always fill up with a superior grade of petrol do you think they tried to con me? I worry about the lubrication properties of the engine oil being compromised by the addition of this cleaner?