Buggeroff6

IiI...I have an 02 sc430 and prob. will change trans/diff/coolant too soon to expect a reply on this old list/thread/server! Just wondering why the writer is so emphatic about getting a syn. trans fluid? DIff fluid? I mean, I use synthetic oil, but haven't heard of any advantages w. diff/trans....did I miss something? Is there synthetic coolant out there too?'