Oster Designer Kitchen center(#5510-20a)?

Blender square drive(post) A.K.A.- part number OS-24771(R)...(the R is a maybe ) has worn down.... this is the post coming up out of the internal motor that spins the blender blades inside of the blender jar. It is worn/rusted....I have seen this part in several locations , but I do not know how to replace it by myself.... . and Im not sure if it is easily done without destroying the internal gearing this square post is- rusted/ attached to. Can anyone or any web site refer me to HOW TO operate? or would shipping it to a repair site in Illinois be better(But not cheaper)