DON'T FLUSH! you want your motor to have lubrication running through it, not harsh cleaners. would you drink soap?! besides, Honda built the damned thing, i think they have a pretty good idea of what it likes and what it doesn't. 54k is the perfect time to switch to synthetic. i just switched my ls teg over at 171, and no problems. the car's running great. i have heard that mobil tends to burn a little faster than castrol syntec, for some reason, but h22s tend to burn oil anyway. just do your regular oil change, with an oem (DEALER ONLY) filter, and your choice of synthetic oil. enjoy.