A doctrine fostered by a delusional, illogical, liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.
If you are looking for the advance because you think the springs are weak (from an earlier post?) try finding a junker and taking the springs off. When PeteN fixed my bike I took the springs of a junk 350 4 I had laying around. The springs aren't listed seperatly in the parts book, and the advance would have been $90.