I have two early (2nd generation?) Corningware Electromatic percolators that are identical except for their lids, which have a few design differences. 

I think one lid may belong to a later version, and am hoping someone can confirm which is the correct lid.  I've attached pictures that show the differences between the lids and how they fit onto the pots.   View full size for more detail.  You can see one lid provides a cleaner fit with no gaps and sits higher on the pot than the other one (pictures #1, 3 & 4), yet when the lids are removed and placed side-by-side, the lid that sits higher is actually shorter than the other one (picture #2).  The lids' openings for pouring/heating element are shaped differently (also picture #2).  The black plastic portion of the better fitting lid is thicker/has a larger diameter (picture #5).

I'm assuming the lid that fits better is the correct one.  Downsizing continues after our move to a smaller and more manageable house, so I'm only keeping one of these.

Thanks Bill.

So the the lid with the "squared" opening is the one on the left in picture 2, correct?  It sure fits and looks better on the pot than the lid on the right.

Thanks for the picture Bill.

I tested out the heating elements this afternoon (I had lost track of which was the good one) and they both seem to work fine.  I think maybe the percolator cord I used before could have been faulty.

I may end up hanging on to both of these just in case the one suspect heating element reverts back to its unreliable habits.

I forgot to mention a difference inside the carafes.  The cup level markings on one are positioned lower than on the other.  The pot with the lower cup markings has a dot to the left of the 4 cup mark.  The pot with the higher markings has a dot to the right of the 6 cup mark.

Could these cup level indicators be positioned as they are based on whether water should be added to the carafe with or without the heating element in place? 

Bill, I came across that same set of instructions after I posted last night. 

I know that if I were to fill these two carafes with all innards removed, say, to the 6-cup level in each one and used the same amount of coffee in each basket, one brew would be much weaker than the other.  That's why I'm wondering if at some point early on, the advice was to fill with the heating element installed.

Also, the instructions mention a red indicator light.  Were they ever actually red?  I've only seen pink (presumably neon) indicators.

Here are pictures of the different markings.  The faint (higher) ones are on the pot that appears never to have been used.  You can see that the 10 is lower on one than it is on the other.