It sounds like you're talking about the shift shaft seal. If that is correct and it is leaking from around the convoluted boot that is on it you'll need to remove the rod shifter connection and pull the boot off. The seal is new so you can either try to tap it in a bit to see if that stops it from leaking or you can remove it and put a smear a little anaerobic sealant around the outer edge of the seal and then tap it back into place using a deep socket or similar. Something that will apply even pressure when tapping it into place.
Double check the fluid level while you're down there also to make sure it's full.