2008 Octavia VRS rough idle.

Hi folks,

Recently purchased my first Octavia. 2008 2.0 TDi Vrs PD engine. Developed a rough idle / black smoke on tick over.  Brought to garage mechanic reckons injector seals need to be replaced, failing that injectors are to be tested , also mentioned oil in fuel filter. Has anyone experienced similar and did seals cure it or were injectors at fault. Don't have the car at the moment to check if injectors were replaced under recall, if they were are they likely to fail again at 140k miles, car has good history and hasn't been abused. Is recall still valid? Any advice welcomed. Thanks.