Six months ago I posted about my HP CM3530 leaving a vertical streak on every page about 1 inch from the left side. This started after I fed special paper in the multi purpose tray after washing my hands without drying them fully which left a drop of water on the special paper and every page printed since that event 6 months ago has had a streak. The problem was worst after the printer did a cleaning cycle and then slowly faded away until the next cleaning, but never went away fully.
I was torn between getting one of the HP Officejet Pro X 70 pages/minute inkjet multi function printers or a new transfer belt (the transfer belt costing significantly more than the 70ppm inkjet MFPs).
Yesterday I again had an important document to print that had to be streak free so I removed the transfer belt to clean it as usual which normally allows the next print job to print streak free (problem resumes after it does a cleaning cycle). However this time I looked at the transfer belt assembly closely to see if I could see the wiper blade as the problem was most likely dirt on the wiper blade allowing a streak of waste toner to make a continuous line on the belt. I was able to see what was most likely the wiper blade and forced an alcohol swab between the belt and wiper blade and slid it across to clean the wiper blade.
Every print since I did that came out perfect without even a hint of a streak, and the printer has done cleaning cycles and many print jobs since.
A 3 cent alcohol swab saved me $700, I hope this lasts but no other belt cleaning method I tried so far lasted more than one print job.
I'd recommend doing this at your own risk just in case it makes things worst, but if you have a transfer belt leaving a streak and are willing to take the risk to avoid buying a new one it may be worth a try.