My mother-in-laws Saniflo Saniplus is leaking at the discharge outlet. The water is coming out between the hard case of the unit and the rubber gasket that the discharge elbow seats in.

SOURCE: Transfer case leak

You mean between the case halves? It is just silicon, no gasket. These are good for the pump wearing a hole in the rear housing and leaking oil. The cure for it is a new rear housing and a piece called a case saver that keeps the pump from doing it again. Taking the transfer case apart to fix it is easy, I can tell you how to do it.

SOURCE: Krups type 889 Espresso machine leaks water

I have found the two parts mentioned in my previous Email on a webpage other than yours, however I have not ordered the parts at this time. If you have the parts in stock, let me know the price.
Once I receive the parts and replace them, I will know for sure if my troubleshooting is correct.

SOURCE: My saniflo (saniplus) is making a slight whirring

Sounds like the outlet pipe blocked, it should be connected by a short rubber pipe , use this to connect a hose from a cold tap and flush the blockage.

SOURCE: Our Saniflo - Saniplus works fine and efficiently

Sounds like a restriction in the outlet pipe, the 2 galls from a flush are OK but the bath or shower is more, especiallly if you have flushed before you shower, try drain unblocking chemicals or flushing the outlet pipe with mains water from a hose

SOURCE: water leak from turboflush saniflo

Check the piping, it might be a loose connection. Also you may want to replace the rubber coupling in between the side inlet and the sink drain. The rubber fitting might have a pin hole.