O-ring leak at heater return to H2O pump

[pkellymc]

Just replaced my water pump for the 3rd time. Last 2 have been "free" 'cuz I bought the lifetime Bosch unit the first time. Had a heck of a time getting the hardline with the O-ring to plug into the water pump, the first time. Second time, it plugged right in and never had any issues. This time, I got the nipple inserted (with much difficulty), and it is leaking..must'a damaged the O-ring getting the line inserted into the pump. Does anyone know the proper size O-ring to use? This latest pump didn't come with one; I think the last one did. Also, does the right O-ring have a round or square cross-section? Thanks!
1995 Orvis, 5.2L, 150K