Glass scale problem

I have a bad spot in the center of one of my glass scales. The DRO
just flutters and doesn't count for about .150". If I get up there
with a laptop screen cleaning cloth and rub it on the glass it works
for a while then starts acting up again. During the period that it
does work it counts perfectly.
I'm Kind of stumped on this one. I've removed the end caps and
looked in with a flashlight but can't really see any debris. I'm
thinking the swab leaves a film on the glass that makes it work then
evaporates over time.
Can the glass scale be removed from the housing or is this suicide.

Thanks
Derek