If the marks are occurring on the front edge of the paper, then I would guess that your paper is bent. I don't really have this problem on the front edge of the sheet. But I have seen it on the trailing edge, and this has to do with the curl that many papers have and the fact that Epson doesn't use a vacuum for holding down the sheet on the 3800.
I have found a solution to these problems though. It is a bit fiddly and time consuming but it works.
You take another sheet of paper of the same width as the one your going to print on and cut off a 2" long strip. Then take linen tape (like you would use when attaching the print to your matboard window) and abut the 2" trailing strip to the edge of your sheet and apply the linen tape to the backside. Now your sheet will be two inches longer, and the traction wheels of the printer will keep pressure on the trailing strip causing the tape to keep the edge of your printed sheet down also. This will prevent the head strikes which are causing marks on your printed sheet.
After you've made your print simply peel away the linen tape and you're done. This workaround can also be applied to the leading edge of your printed sheet if you're having problems there. On the leading edge you will have to remember to tell your printing software that the paper is 2" taller and move the top edge of your image down 2" so that it only prints on the main sheet instead of the extra leading strip.
This technique works on any printer with traction wheels that is having head strike problems on the leading or trailing edges of your sheets.
I am encountering what I have learned is a common problem with the 3800.
Using mine to make editioned fine art prints of drawings/paintings on 17 x 22 sheets of Hahnemule Photo Rag 308gsm, I am getting bits of black ink on the corners of the paper that render the prints worthless.
The art is all black (using abw mode), with a lot of white space on all sides. Therefore, the corner black marks on my prints are even more infuriating than they might otherwise be. In some cases, I can gently shave it away, with a razor blade, but in other cases, no.
I am using the trick of bending the corners back a bit before loading the sheet, and that sometimes works.
I can't in good conscience get in to arbitrarily trimming prints down from their advertised sizes. Trimming also makes the continuity of presentation more challenging.
Wasting sheets is expensive, time-consuming and frustrating as hell.
A fine-art photographer friend of mine showed me the bend-the-corner workaround — his gallery had complained about certain messed-up edges he wasn't able to hide — and also told me that when he inquired directly with Epson, they "wouldn't really go there." Hmm.
Has anyone found a RELIABLE workaround to this problem? I'm not looking for "I've never had this problem" responses. It exists, and I really do need the help of someone who has experienced it, and has figured out a way to deal with it.
Your help is appreciated.