Xerox 510 ADF Page Margin Shifting

Hi,
I have a Xerox Documate 510 with an auto document feeder. When I'm feeding
in multiple pages, the top margin isn't always set for the top of the page.
Generally, the first sheet feeds properly. The other pages feed but the
scanned image has from a .1" to .25" of white space at the top before the
actual scanned page starts. Sometimes this pushes the bottom of the scanned
image off the page.

What I've been doing is setting the scanner to legal size paper when the
scan begins and cropping the images but that kind of defeats the purpose of
a document feeder. I tried cleaning the scanner and reinstalling drivers but
I keep having the same problem. Any idea how I can fix this problem?

Regards-Michael G.