piston

Hi all, First post so please be gentle :) Bit of brief background, I owned a w204, used, 6m old, 4k, coming up to 4 years ago. Had to sell due to change of circumstance. Been in love with Merc ever since. Fast forward to mid to late 2018, suspected epilepsy, obv couldn't drive. Last month...

Can anybody answer my question. I have a 2003 V220 that has just had a major service. The garage told me that the pistons may have gone as there is black smoke coming from the manifold when I put the heater on. Car is running perfectly otherwise. Anybody know if this is correct or could be...