well if youre smelling diesel then check the seals on the injectors and also the return pipes

the return pipes are held on by nothing more than friction, if they have been disturbed they could have came loose. you say the injectors have been tested as well? check fuel unions and push clips, if you follow both the pipes form the fuel filter, check for leaks and what not you cant go wrong, only tricky bit is at the fuel pump as its tucked in behind the EGR cooler.

will have a look tomorrow but can injector seals cause white smoke to occur? There's no "puff puff" noise from the injector area but I can see some sort of liquid there. Put a screwdriver to touch it and it was black. Not sure if it was oil or diesel.

The liquid is most likely oil. Either from the injector seals (were those changed?) or from the oil scrubber filter (not sure this is the right name for it - it's the black plastic thing with a hose comming out of it). Usually it is from the injector seals.
White smoke on the other hand is usually unburnt fuel, so I would check inlet manifold for air leaks, MAF and IAT for oil, or turbo actuator.
Now that you have the elm interface, you could do a test run with Forscan recording parameters, and see what is actually going on.

Just a thought, do you have a DPF/FAP? Try checking with ForScan for "Distance since last regeneration trial" if you do. It might be that your car isn't finishing the regeneration process, but keeps trying to do it over and over again, and what you see coming out is just unburt fuel.