After the Banjo Bolt is Cleaned check the Boost Pressure you are getting.
You man Need to adjust the Tension on your Waste Gate Spring to bring the Boost Pressure up if you are not making good pressure.
I have been wondering if You are also having Fuel Supply issues due to an old Fuel Supply/Lift Pump, Fuel Pressure Relief/Over Flow Valve, Fuel Tank Vent issues.
If you can scrounge up the 5mm O-ring Fastlane used to sell a Valve Kit for the Fuel Supply Pump. But, that kit lacks the little O-ring.
Info in the DIY section.
ForceInduction lives somewhere in that State. He is the Moderator over on the
Diesel Discussions - Mercedes Forum - Mercedes Benz Enthusiast Forums Forum if you need answers to some specific questions.