C253/353 black IU failures

Has anyone else been experiencing premature failures of the imaging units on the C203/253/353? We have been having the same problem on multiple machines. It starts with a dark line at the front that can "usually" be cleaned with the charge cleaning wand. Eventually, sometimes a week, sometimes several months, go by, the line comes back and it can't be cleaned and the IU has to be replaced.
We are currently using aftermarket toner.
Any thoughts or suggestions are welcome.
I disassembled one today and the charge grid is covered in toner from about the halfway mark to the front.
Thanks.