Thanks for your replies. We have not had any leaks coming through just the middle of the roof, but have had leaks around flashing, etc. From one leak by the chimney, I think it was b/c the flashing was not properly installed.
So, it sounds like the key indicators are:
a) does the tile still have coating on it? (ie-not smoothed, but still bumpy with little grains)
b) are tiles flat? not curving, etc.
Also, from the inside, the decking looks good. I don't see any stains or leaks, but is this test realiable as the damage would be on the top of the decking?
Also, it sounds like a "10-yr roof" can last longer? In trying to search the Web for this, I can't find any 10-yr shingles, is there such a thing?
THanks!