I've had a Silca for almost 20 years with no problems.

Get a head like this for both types of valves.

http://www.westernbikeworks.com/prod...il.asp?p=SNJWI

I'd take off the black part which is designed to push onto a presta stem and be pulled off. I've always had a concern about breaking the valve. At the very least the rubber washer wears out.

Instead take off the black section and replace it with one of the little presta/schraeder adpaptors that the LBS sells for about a dollar. No more pushing or pulling on the stem and a connection that screws to the stem so there's no air leak. Even most threadless stems have a few threads for the useless plastic cap to screw on. For Schraeder, just unscrew the adaptor.