hi i have noticed my golf had a little leak so i traced it back to the water housing it had a small crack in it so i bought a new one but cant get the thermostat sensors in and need a rubber gaskat
plz help

You mean the black or blue temp plastic sensors?
If you are they sit with a rubber washer and held in place via a circu clip. The pressure of the water will seat the sensors better when the engine is running.
A pic of what you mean would be better fella?