hard to tell from the pic yo posted. do this: Take the lens off, open the camera back, set the camera to 1.500 of a second or even 1/1000, hold the camera up to the sky or something evenly illuminated, and fire the shutter. Look at the shutter opening when it is briefly open -- it should be fully square, even all the way across as the shutter slit travels.
If it is dark on the side to which the shutter travels, that means the second curtain is catching up with the first curtain because the first curtain is slowing down, probably gunk in the channel in which it slides.
Time for a clean if this is the case.
If the opening is fully square and even, then your problem is somewhere else.