Apocryphal Quote Alert

Justice Louis Brandeis said that Robert Jackson "should be Solicitor General for life." Or did he? I don't know.

I can't locate the original source for this quote, which often appears in accounts of Jackson's career. (Indeed, I once quoted this line in something that I published about Jackson.) Now I'm wondering if this is a false quote. If anyone knows the original source, I would be much obliged. 

UPDATE: The evidence is mixed. Justice Frankfurter and Tommie "The Cork" Corcoran both told Jackson that Brandeis told them that he made this comment to FDR. That's not totally convincing, but it's not unconvincing.