rebuilt tranny and leaking water pump.

Good morning.Iv seem to be having the worst luck lately:banghead:. I have a 96 seirra 5.7 v8. I just had the transmission rebuilt a couple of days ago. Now im pouring coolant from somewhere on the waterpump. Im just wondering if it was anything the mechanic could have done while he was rebuilding the transmission ?
`Thanks in advance for any replies.