Hi ldatlof,
Yes, C21 is the line to ground capacitor. I had been ordering Vishay caps from Newark but they don't seem to have them in stock anymore. The value of the safety caps used in the sets originally creates more leakage current from line to ground than is acceptable by todays standards. A smaller value capacitor is usually used as a replacement. I have been using the 4700pF cap in the 440L series found on this datasheet:
http://www.vishay.com/docs/23092/aclinecp.pdf
Hope this helps.