2003 Ford Mondeo omissions failed mot

Hi

I'm asking for my mum. Her car has failed mot only on omissions test. Failed last year on same thing but she was told to put smoke stop stuff in oil. She also added something like that in petrol. However, this time black smoke/liquid is flooding out still. She's taken it for a good run, and really revved engine up but no joy.

She cant afford a new car and so u said id get on here and see if anyone has any advice to get it through the mot.

Any help is greatly appreciated.

Thanks

Kerry