Epson Expression 836XL Scanner issue

[TwoPynts]

My wife is a watercolor illustrator and I scan in her work for her on the A3 size 836XL scanner. Some of you may know that while standard size scanners are relatively cheap, the larger ones are not. A decent new A3 scanner starts in the $1500 range, something we can't swing right now. I tried a $160 Mustek A3 scanner, but the scan quality wasn't acceptable. I just lost a bid on a newer Epson on eBay, and rarely do I see good A3 scanners offered there.

The 836XL has given us years of great service but just the other day, a brown line started appearing in the scans, looking a bit like a smear. It is near the center of the scan bed and starts gradually in the middle of the scanner and increases in density and very slightly in width as it travels to the bottom. There is nothing on the glass that could be causing this and I see nothing else visually that would account for it. Can anyone explain this problem and does it mean the scanner is near the end of its life? Scans in the top half of the bed are still fine, but that is not enough usable space for me.

Thoughts anyone? I use Hamrick VueScan software and a Ratoc SCSI to Firewire adapter since my '07 iMac doesn't have SCSI capability. But I've been using this set-up for a while so I don't think that would be a factor.

Thanks for any insights you may have.