NewtwoMB

Hi, I just had my car government tested (as its 3 years old now and this is mandatory here in the UK) and, while it passed, I received an advisory on the right side rear shock which was said to have a "fine oil mist" on it. Anyone help on this? Do I need to change it soon? Is this a DIY job or should I take it to the dealer? Its a Sport model with the shocks that adjust to the road conditions but NOT with the Active switchable suspension. Thanks for any advice.