Fixing my cool new/old water pump.

As my new trailer is missing the lower kitchen section, I have been keeping an eye for missing parts. I have a stove and sink, but needed a few latches, tap, and pump. I haven't decided yet on hot water so the tap can wait, but yesterday I bought this very cool vintage pump from a guy online I know who sells vintage parts. I am doing a starburst theme in my trailer so it was an instant yes decision to buy it. That being said, he says the pump works great in terms of pumping out water, but it leaks a bit around the nut at the base of the pump when its pumping water. Does anyone know how to fix this? Should I expect to rebuild the whole pump? I remember someone on here saying they have rebuilt a pump before...
Here are some photos.