Greetings: As I suspect my (differential)final drive is starting to leak AGAIN on my 85 5kt, is it OK to use MOBIL 1 70w90 synthetic in the bugger? These days I avoid the dealer if at all possible. Also, would someone know hat sort of tool is used to remove the plug? About 50 k miles ago I had a shop replace the seal--it took them 3 tries to get it right. Thanks in advance!! RC Ringlien