Hi @xpd,
Flick me a private message with the address you think it is, and I'll see if I can locate it from my list of units for that street address.
I think (from memory) the G-140W-C is the Type 300 ONT, so the serial number sticker will be located on the side panel (when looking at it mounted on the wall).
[EDIT: just noticed the post 3 minutes before this saying it's resolved. Sweet!]