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If you switch a direct link to a 302 redirected link, you're absolutely going to lose the value of that link. See this 2010 post on SERoundTable about ways to retain that link value and pass affiliate IDs: http://www.seroundtable.com/archives/022446.html - read the comments on the page as well. As a sidenote, If I recall correctly, I have seen it indicated either officially or unofficially that Google doesn't 'like' the passing of link value through affiliate links - I think they rightfully consider them a form of paid links.