It would be unlawful to deliberatly vent it to the atmosphere.
You wouldn't want to get them California enviro-whackos on your case would you??
Fact is though, if it hasn't worked for several years, it probably has all leaked out anyway. Just locate the schrader valve and give it a quick touch (as you would a tire valve) and see if it has any pressure. If not, you're clear to disassemble. If it still has pressure, you would legally have to take it to a shop and have the remaining freon recovered.
Glad to hear you're going to have the old Benz back on the road.
