I don't have the AZ p/n. They're listed on the site here: http://catalog.peachparts.com/ShopByVehicle.epc?q=1983-Mercedes--Benz-300cd-Climate--Control&yearid=1983%40%401983&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6169%3AED%7C10000135%3AMBC%7C1496%40%40300CD&catid=242213%40%40Climate+Control&subcatid=242239@@A%2FC+Pressure+Switch&mode=PA

A google search points points out other sources.

I'm sure it's possible for the switch to leak, but I think the failure modes would normally either be a bad pressure/electrical failure OR a bad O-ring. A "leaky switch" that dumps refrigerant is probably a distant third.