If it is leaking from the pipe that attaches at the back it is probably the rubber seal that goes on the pipe and is then inserted into the waterpump (held in place with a short bolt).

If you are sure it is that point leaking you can most likely detach the pipe from the clamping point on the engine and change the rubber seal, then reinstall it.

A little silicone and a well cleaned pipe will allow the pipe to slip into place without ruining the new seal. Install and tighten the bolt.

These are available from internet parts houses in a kit that includes the mentioned seal, the donut like seal on the top of the pump as well as the gasket between the pump and the block.

More likely is that it is coming from the seal on the top of the pump that is pressed against the bottom of the head. If that seal is leaking it requires that the pump be removed to replace.

If your pump has seen a long life it would probably be best to replace it if removal is necessary.

Randy