Glad to help.
Don't rule out leaking around the valve stem, or the schrader valve (interior component of the valve stem).
If you decide that its not the valve stem, see if you can arrange to inspect the wheel after the tire has been dismounted, I had a couple spots that had raised white powder looking spots of corrosion, I could see it leaking there.
E39 - 1998 540iA Sport (11/97 Production)
E30 - 1989 M3 (44k miles)
1979 Triumph TR7, still have my first car ;-)
E21 - 1980 320i (sold at 130k)
E23 - 1986 735i
I am a BMW Car Club of America member, are you? <a href='http://www.bmwcca.org/' target='_blank'>http://www.bmwcca.org/</a>
<img src='http://members.roadfly.com/kowached/bmwcca1.gif' border='0' alt='user posted image'>