Losing coolant, but where from?

[kris]

I've been losing coolant for a while now, but quite slowly. As in, ive had to top off two or three times in the last four months because my dash told me it was low. I haven't had an issue with overheating, I just had an inspection a couple weeks ago and emissions were lower than last time on all counts, I haven't noticed any smoke, no coolant in my oil or oil in my coolant, no leaks that I can see, and I believe the water pump was replaced 25k miles ago during the engine rebuild. I will add that the engine rebuild was done by my cousin (very capable) but on my uncles budget, who wasn't planning on keeping it long. The first thing I had to do when I got the car was scrape rtv off the valve cover to replace the gasket.