Very knowledgeable transmission guy discusses the GL5 myth that it damages the synchros in our transmissions. While the video isn't about a 4g63 transmission the discussion (or his experience over 1000+ transmission rebuilds) about GL4 vs GL5 oil was very interesting. I've used GL5 in my trans for the longest time with ZERO issues. Enjoy the video. Discussion about lubricants begins about 11:20 into the video.