I have ran Rotella in many different bikes including GL1500-1800. IMHO the 5w40 is a little low or thin in heat & hard engine breaking. Once on a trip from IL to Ca ridding in July heat and a lot of engine breaking my 06 GL 1800 used over a quart of oil. I checked the oil level when I started home in Ca and it was between the marks. When I got home it was barely showing on the dip stick. Not good and since I have stayed with 15w40 Dino. My foot could never say T6 shifted better. Again not wanting to start an oil war, and as pointed out I know of no engine failures related to the weight and brand of oil you choose but I think my experience is worth noting.