http://www.renntech.org/forums/index.php?showtopic=659&st=0
All you need to know is above.
E-gas started in 2000 and there have been 3 sensors used. 1997-1999 are not e-gas and they use a different sensor.
The first e-gas sensor had a flat bottom. The second started in January 31, 2000 had has a hooked bottom. The third is a replacement for the second as the second was discontinued.
You cannot swap between the first and third versions unless the DME is reprogramed.