Klaus, I had a leak on my '95 850 waggon on the Schraeder-valve, and was able to "fix" it by simply buying a Schraeder valve-core wrench, and tightening it. It seems that these valve-cores sometimes work their way loose, and then leak. You can also entirely remove the core (of course, immediately loosing all pressure), and put in a new one if the rubber parts have perished. In my case, my AC went from one to two weeks between recharges to an entire year. A cheap, and stress-free solution, if it works!