Hi. The 7s is a good camera - worth fussing with to get right.
Buy a seal kit from Jon Goodman - he goes by the name Interslice on eBay. His seal kit for the 7s comes with easy-to-follow instructions, and, as a bonus, he throws in instructions to clean and align the viewfinder. All for just a few bucks. Takes an hour or two for the whole job. He also sells a clever battery adaptor that converts the camera from the dread 625 to the commonly available 675 hearing aid battery.
Good luck,
Mike
PS - You are way ahead of the eBay game, in that you can actually put your hands on the camera prior to buying it. With that in mind, and no shipping cost, $40 is a good price, if you think the camera works OK.
Make sure the lens doesn't wobble too much (they all seem to move a little) and that the shutter speed and aperture rings move freely on the lens. Don't discount having a functional meter - the one on mine is quite accurate and handy. The meter scale in the viewfinder is in EV - once you know what the EV is, the camera is designed to let you manually use any combination of speed and aperture that gives you the same EV by rotating the controls together. Kinda cool!
M