Leak at side of engine

1996 Olds Achieva,4cl.,quad4,120,000 miles.Hi,i asked a question about this leak yesterday.....well, I was at a different location,on the leftside of the engine where the upper radiator hose,and heater hose connect to a plastic housing that bolts on to the engine,right below the oil sending unit..I had originally seen on the plastic the word,"thermostat" but couldnt read the rest(I need new contacts),Well, I got it off and it said,'thermostat located at water pump"..and this made me see some sense in your reply.....!!!lol.Now,since I now found our there was no thermostat in it,I see whay it was leaking....the plastic housing seems to have some kind of ceramic-like material that has a groove for an o-ring,but it was broken badly,so the o-ring was loose.i am in the country doing this,so I freaked out.But I used the gasket for the thermostat to try and see if that would seal it,,,,,and am still checking it out.But what do I need,a totally new plastic housing.and a new 0-ring??It looks like the ceramic like material is bonded to the end of it where it goes in the engine(and seals with the o-ring),but I'm not sure>I dont even know how to describe to the parts people what I need,except to describe where the problem is.So,bottom line,all I need to do for now is get a good seal here,and see if the water leakis fixed. Thanks,oh, and thank you for the last reply Ben