In my garage there rests a jug of Mobil 1 15W-50 which I bought two months ago intending to use in my Bimmer, which has been garaged since my daily driver's become a 300DT two weeks ago.

The 300D really needs an oil change, and I'd like to do it this afternoon or tomorrow. The question is, should I use the 15W-50 or get some turbodiesel oil from the truck stop? And on the same subject, should I be using synthetic or dino in a 617 which has been running dino its entire life, and hasn't had its rubber changed in ages? It's currently running well enough, albeit a 1qt/1000mi leak, that it'd kill me to start a lot of other leaks by unclogging sediment with synthetic -- if that isn't just an old wives' tale, that is. If it isn't, she could sure benefit from any advantages synthetic provides. I'm going to be driving in 100+F weather all summer.