Leak at discharge port on waterfall pump

[akg0626]

I have a leak on my discharge port on my waterfall pump.... the sealant does not look solid (sealant is probably a couple of years old)... do i have to actually unscrew the pvc pipe that connects to the pump, or can i just put new sealant around where the pvc pipe connects to the pump?

If so, what is the best sealant to use?

Thanks!!