Problems with Epson scanner

I own an Epson Perfection 1200S scanner. Lately, I've noticed that the
horizontal margins of my scanned images are not straight. For example: if I
scan a document, the bottom and top margins show an inclination and I have
to rotate the image with an image edition software to get it straight. I
though that the problem might be due to a disaligment of the scanner's cover
which moved the document slightly when it coverd it. However I discarded
this possibility after having secured the document in place with scotch
tape. I haven't took the scanner to Epson for repair because I fear that
repair will be as nearly as expensive as a new scanner. Any thoughts?