The only engine in this car, I think, was the 3.1.....there is no timing belt cover, since this has a timing chain.....I've never seen this leak coolant at the timing cover......
As for the w/p, possibly the easiest of all to replace.....whenever the system is opened, it has to be "properly" burped of all air, before it is given back to the customer......
For you to be adding all that coolant, sounds like the mechanic dropped the ball....these engines are known for lower intake gaskets, and if allowed to leak too much, can cause head gasket problems....
If I remember right, the coolant level sensor is located in the radiator.....if the light is coming on and the radiator is full, it could need replacement.....they become contaminated and also need a good coolant flush...
But keep an eye on the level of the reservoir......always check it first thing in the morning before starting it....if it's dropping, and it was properly bled, there is another leak....