"Never put synthetic oil, transmission fluid, or differential fluid in it.... if you want to start having problems, just start using synthetic fluids... they loosen up stuff that shouldn't be loosened and that car wasn't designed for use with synthetic fluids."

Those were the words of my mechanic when I mentioned to him, the fact that I intend to use Amsoil synthetic fluids bumper to bumper in my 1984 300SD. I searched all over the forum and spent about 40 minutes browsing through search results and I've seen nothing but praise for Amsoil's synthetic oils and ATF. He really confused me because I had put Amsoil fluids in my 1989 Mazda 929, my 1990 Honda Civic and in my 1999 Toyota Avalon and they all run well without any issues. Additionally on the Amsoil website it is stated that the diesel oils they have a suitable for use in Mercedes-Benzes. But then again, my Mazda and my Honda have been using the fluids for over a year but I've only put on about 4,000 miles on each of them (they aren't daily drivers... just cars I bought to have for fun). I've never had any problems, or ever heard of synthetic fluids being bad for ANY car.

So right now, I am thoroughly confused and I'd greatly appreciated it if someone who has been using synthetic fluids for lots of miles spoke out to help clear my mind!!