I don't know the history and can ID the fittings. I was leaning toward a complete evac and new freon/oil. I'm familiar with the Saab setup but suspect that MB may have a different arrangement. e.g. I don't know what TVX is or an ETR. It may be something I know with a different name.....I'll have to go over the documentation.

I have a vacuum evaporator and a set of professional gauges with hoses and fittings for 134a and R12. I'll check out what I have and get back to you. I am glad to see that your suggestions confirm the way I was already leaning.