hello everyone. just recently joined the site after lurking for a couple weeks. who knew oil was such an involved science? i have two cars '01 bmw x5 65k and a '97 MB C280 91k. i just order the Auto Rx. i just purchased the BMW. the oil does not look like it has been changed in quite some time (almost black). just had to add 2 quarts the other day because the oil light came on. should i change the oil before the Rx application since it recommends the oil have 1500 miles sevice life? and after the applications which oil should i use? i have done searches on different oils and GC and M1 seem to be highly recommended. but which weight? i live in D.C. so the summers are hot and the winters are cold. any help would be appreciated. also i am thinking of using the LC and FC also. thanks.