Stay with Freon. Most of the forum agrees that you will not get enough cooling in the SD with R134a. The original compressor is R4 and that is what bought when I replaced the compressor in my '81 300SD. Several folks say you should upgrade to a Sanden compressor; if you do be sure to purchase the special support system - it is different from the R4.

For the FSM I have a two CD set that I bought from someone on the forum; it is very difficult to use but it does still work. I have to use a computer with Windows XD and I have to use Navigator (not I.E.) to open it up. That said I have never been happy with it and only go to it when absolutely necessary. I am really an old paper book guy and with I had a real paper manual. You might get your new computer to emulate XP and get your CD to work; that is a special feature that some of the newer products like Windows 7 had and I do not know if Win10 has it or not.