Hello. My name is***** may be able to provide you with some additional assistance.
I did read through your question and your discussion with the previous expert. So if I've missed something I apologize. It sounds to me from what I read or at least as I understand it, that there is a streak on the transfer belt, but it is not causing anything unusual on the output. If this is the case, then it is very likely to be just a leaking or misaligned toner. You would only really have to be concerned about it, if it is in fact not showing up on the page, if it was causing a mess inside the printer that has to be cleaned up even if it's occasionally. There should not be that much toner coming out onto the transfer belt, although it is not uncommon for there to be some on the edges because the very edges do not get transferred and there is sometimes buildup of toner there. So if they are coming up on the belt – and on the right side of the belt specifically (I'm not sure if you mentioned the side of the belt you are seeing it on), then it's usually nothing to worry about and you can just leave it like that with no adverse effects. Also, if you've received a message or do receive a message about emptying the waste toner cartridge or been, be sure to do that at that time. Sometimes waste toner can roll back onto the transfer belt if the bin is full.