We use white vinegar every once in a while to help with calcium buildup, in conjunction with a calcium rinse, as we have some issues with it. We tend to run an 890x627 velvet sheet sometimes for weeks on end, then go to a 720x1020 gloss and have watering issues about 3" in from edge of sheet. The smaller sheet leaves a residue that has absorbed into the rollers and they are probably more at the point of replacement, but this residue tends to promote the transfer of water resulting in a slight but very annoying washout in those areas(more prevelent in the magenta and cyan decks). Micro tuning the profiles and tweaking the rollers gets the job done, but is not a solution in this case. The copper rollers also have a discoloration and is part of the problem...
If you do use white vinegar to alleviate the problem (and it does help!!) ensure that you clean rollers thoroughly first, then wet them down with the vinegar, inkers and dampeners engaged (use plates you wont need again) idle it for approx 5mins and most importantly, WASH IT OFF WITH HOT WATER. Use plenty of water and really give it a good going over... its not a total solution but will help some...