There are a number of reasons why you can get the black smoke on acceleration...dirty, or partially blocked air filter...faulty, or dirty MAF,...incorrect grade of fuel...faulty injectors...fuel pump not correctly set and the list goes on. Start with the simple stuff first and work your way up...just ensure the motor is heating up properly before you do anything...a cold diesel will almost always over fuel itself.
As identified by Mac, the oil in the pipework is down to the turbo seals...dirty job to rectify, but not impossible. Last time I had this problem, I just sourced a company which specialises and had an exchange unit fitted...simple job and not all that expensive.
