I have removed the old, broken pump and I am installing an Enduro Doctor rebuilt pump.  When I am seating the pump to the case it seems like there should be a gasket in this area.  Am I correct?  There wasn’t one on the removed pump but it looks like there should be one.  Thank you for any help.

Yes, super common gasket...  fits every Yamaha two stroke pump I can think of.  If you have a local dealer they may have one in stock or you can order one from someplace like RMATV-MC and have it in a day or two.

Also check packaging and maybe contact DEET to make sure there wasn't one in the box with the pump.

Thank you!  I couldn’t find any diagram of it in the Clymer manual.

Most of use the online parts diagrams for reference.  They aren't always 100% correct but they are very helpful. 

You could also use the factory manuals in the tech library here...  the basic one is the 78 service manual.  79 had a few differences like leading axle forks but basically the same bike.  There was a 79 and an 80 supplement to the manual.  Tech library has the 80 but not the 79 supplement...  the 78 and the 80 supplement will cover about 99% of your bike.

Here's a diagram from the 78 manual.