Here is a suggestion to try. You say that the press was used.You have cleaned and re-set the sliders. Check to see if the original factory painted seals (red or green color)on the screws that are at the sides of the fountain have been broken, if that is still possible. The original blade would have been set up with a gauge at the factory against the fountain roller and then locked and marked with paint. I was with a technician on a call once that was trying to get a good balance on the keys. He goal was to try and get an even ink film setting setting with the keys opened around 20% and 70% across the ink fountain roller. He would adjust with an Allen wrench at the 20 % value .He then would open them to 70% and check the ink film and make the same adjustments at higher ink setting. It may not be perfect but may help.Try this and then see your results. One other thing to mention, and I am sure that you have tried this. Check your side cheeks and see if they are OEM. Sometimes after market product looks good but doesn't quite cut it. I really saw this problem more so with after market ink foils. Hope this has been of some help.