[morzh]

In addition to what Skyscraper has noted,

1. heat on "Low" using a heatgun. In case you do not have "Low" (some heatguns have cool and hot, and some Low and High) use high from a distance. I use "Low" for 10-15 sec, equal time every side.
2. Use a blunt instrument like a small Allen wrench. Sometimes the tool gets in between the two caps that are inside and if it is any sharp it can cut through the warm tar and you get a hole and the tar block still stays inside.
3. If it resists, heat one more time, do not force much.
4. Leave the cap in place (do not unscrew) when you do it and do not unsolder the wires - makes it so much easier, just cut the think wires coming from inside the block (!!!! - very important unless you want to deal with a mess).
5. No regular caps are NOT fine. Use only Y-rated capacitors.