If it is leaking from where the jar screws into the pump area you should see an o-ring in the pump area that seals the jar when it is screwed on. If you do not see the o-ring you need to find it - sometimes they come out of the grove and you don't realize it's not there, or you need to get another one and install it. if it is there remove it and clean it and then replace it back into the groove. If you want to you can use a small amount of vaseline on the o-ring to help with the sealing of the jar
Hope this helps