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My digital cam is on vacation so a scan of a sketch will have to do.
Should there be an o-ring at the base of the water pump drive on the front of the timing cover? I don't believe there was one on there when I removed the old pump but I know that someone has been in there before. The colored-in portion behind the splines appears to be some sort of seal but it's hard to tell. Definitely doesn't appear to be a worn o-ring or anything.
The colored-in portion on your drawing is the o-ring (P/N 12553792; there's another identical o-ring on the water pump output shaft). Your drawing looks pretty accurate: it appears that your o-ring is flattened out just like mine was; at first I didn't realize it was a rubber o-ring-- looked more like some sort of plastic bushing. There is no o-ring at the base of the shaft on the timing cover.
My new ACDelco water pump came with an o-ring. The original one I took off didn't have it ('94). I used never-sieze on the splines, as there was significant corrosion at 97K miles (I almost could not get the coupler off the old pump!).