heidelberg SM 102 Oscillation

We have a 4/color SM102 that we can nort get to print equally from gripper to tail . We have tried changing the oscillation but have not been able to cure the problem. The unit has all new rollers and are set to the book.

 

Does changing the oscillation timing changes the position of lets say lower density to middle of the sheet or somewhere else or it remains the same?
How much difference is there from gripper to tail?
Is it happening with a particular ink/color?

 

to further Asif's questions, does the coverage fade evenly (across the whole image) from lead to tail, or more one side than the other? What model year is the machine? Rollers set to the book...but did you experience any difficulties achieving proper stripe on any roller position? I'd be curious to see a breakaway dry solid.

 

It is happening in our Cyan Unit with a density difference of 12 -15 points from front half to back half of sheet

 

Is it changing position when you change the oscillation timing? If not then there may be something else wrong.