I had my oil changed today and the guy told me my radiator fluid was low and recommended I get the flush, fill, etc. Is that really needed? Should I just top off the fluid myself or should I be worrying about why it lost fluid in the first place? Thanks!

 

If the radiator has less coolant it would get it from the reservior anyway - I would disregard the dealer's observation if the reservior has enough coolant with engine cooling after a long drive.

Remember, if you want to fill the reservior go for a 50-50 ratio of Prestone (green coolant) and soft water (distilled water).

Last weekend I drained the coolant from the radiator and filled with above combination. ENJOY!!!!!

 

http://www.motorvate.ca/mvp.php/502
it's for 4th Gen Max, but it's quite the same as 5th gen.