2007 Ford Explorer Transmission Seal Leak

I had 176k miles in 11 years on my 95 Explorer (with only the replacement of the transmission at 100k) when I gave it to my sister.  It now has 200k miles on it in 2010 and my sister is still driving it!   

I bought the 2007 Explorer and already have 60k miles on it and have not had to even buy tires yet and have done nothing except oil changes and tire rotations to date.  I liked the size of the '95 better for loading the kayaks on top but otherwise I'm still a huge Explorer fan and Ford girl!  However, today, my mechanic said to take it to the dealer to look at a minor transmission seal leak.  (Nothing on the garage floor yet)  I don't see transmission leak as a known issue on any Explorer blogs for the 2007 V6 and was surprised to hear of a problem given my longevity with the '95 V6.  

I do see I am supposed to have the dealer replace transmission fluid at 60k miles so I plan to do that.  I am wondering what I should expect to pay if a transmission seal has to be replaced or if there is a known issue.  The mechanic said it is not a significant leak but have Ford look at it.  Thoughts?  Is this major or minor?  
Thanks,  LG