Subject: Re: correct juice to use in diff of '88 90q? >I just replaced mine with Mobil 1 75w90 GL5 synth oil. I thought that GL-4 was the correct stuff, being formulated for the bronze/brass (?) synchros. I think it is for the Redline, and that the GL-5 causes problems. Is it any different for the Mobil-1? Should the GL-5 be flushed and replaced? Mark