In all honesty, your connections should be tight enough to not worry about this. Most leaks are caused by water's unique surface tension, e.g. "creeping" caused by water sliding through the tiniest cracks. Flow actually creates currents that slightly interrupt creeping, and you will occasionally see people who have solid, watertight systems that dribble when they are unplugged for movement to LAN parties.

Turning off the pump for any extended period of time is dangerous. If Windows suddenly decided it was time to do some maintenance at 3AM and brought the cores up to load, you have a major issue! Either keep the pump on, or take the system down (standby at least) when you aren't using it.

That makes sence. Thanks.

I would not recommend shutting the pump off for any reason while the computer is on. I used the XSPC rasa 750 RS360 kit on my 920 as well. It also cooled the motherboard and a GTX 480. I ran it 24/7 for about eight months with an overclock of 4.2ghz on the cpu and 900mhz on the gpu and never had any problems... other than it heating up my room.

Though this is just from my personal experience with the XSPC gear. I would not worry about the pump wearing out any time soon. Make sure you are monitoring your temperatures or maybe having a flow meter to put your mind at ease.

Did a vid: http://www.3dgameman.com/q-and-a/393/turn-water-cooling-pump-when-system

why would you leave the computer on or at least not on standby if you aren't using it?

I literally turn my PC on to play games or maybe to do some tweaking benching... then I turn it off.