Common spot on the 3.0's for this leak. Do a search on this section on water leak, or use google, and you will find several links, youtube vids, and write-ups on it.
As to it being a major or minor fix, I guess it's up to either you doing the repair (my labor is cheap, for me doing work on my vehicle) verses paying someone to do the repair. Most of the accessories have to come off to get the timing cover off, scrape and clean all mating surfaces for new gasket install; this all takes time, and that's where the cost runs up. Most shops in the central Florida area charge 90 bucks an hour, just for labor.
I searched on this section, and found several; here's one example:
2003 edge timing cover gasket