Yup, happened to me with a 530d. Luckily I knew what was going on and got rid of them, idiots. TBH they'd point it out after doing it.Not been trying to sell it have you? Adding oil to the water is a favourite scam of some unscrupulous potential purchasers in order to get the price down.
If nobody put it in there you need to get to a garage as soon as possible buddyHi all help would be massively appreciated, I’ve got a glc 250d OM651 engine which has got neat jet black oil in the coolant tank, any help would be greatly appreciated , it’s 2016 with 35k miles