318d engine squeal

[La-spoon]

Picked up a 318d last week from a dealer, 2011. Engine was squealing. They said they had just steam cleaned the engine which was spotless and sprayed some silicone spray on it which stopped it. Noise returned next day and we have sprayed it a few times and it goes away for a short period but comes back. Should I be worried or is it more of annoyance than a major issue. Just wondering whether its worth going back to the dealer to fix (if they will). Thanks.