The seat is the obvious and defining focal point of any recumbent bicycle. Unless someone can provide evidence otherwise, I will go out on a limb (a very short and sturdy limb) and say that no other recumbent has been produced, either homemade or limited production, with as high quality and functional seat as the original Avatar.
Unfortunately, 40 years can put any leather product to the ultimate test. Despite storage in controlled environment and lack of abuse/use, leather can still deteriorate. Dry-rot can exist, even though a seat looks to be in good or even great shape. That is undoubtedly the case with many of the original bikes that remain.
The following information is provided to help anyone seriously considering replacing the original with a new seat made to the original standards.