Question
I am not informed at all on the subject, but have four 60+ yr. old oaks on my property in Central Florida. The jewel of them all - front and center to my home - lost a limb 10 days ago. 20" diameter, 40' long, across the roof of the house. A second yesterday. From the same junction / "Y" in the main trunk. This one 30+" in diameter, again over a different part of the house. A large heart shaped breakoff now exists about 20' off the ground. There is noticeable rot from the break, into the center of the tree and likely clear to the bottom as I can see an opening there soft wood within. It has been an eventful 10 day's, but I sure would like someone to convince me that I can save this tree. Can I scrape and fill the cavity? Bolts, harnesses - anything?

Answer
Trees like humans do get old and as they do will start to have more and more problems. If the tree has rot showing 20 feet up the trunk you can bet the tree is hollow down to the ground or at least the inter wood area is rotting.  The inter wood of a tree is dead and if there is an opening for fungi to enter then rot begins. The same thing will happen if you take a wood board and leave it out in the weather over time fungi will rot is. The living part of a tree is the cells just under the bark called the cambium layer--as the tree grows the cells lay down wood inside and bark outside.  
The health of a tree is determined by the fullness and color of the foliage. If the tree has a full set of leaves and does not seem to be thinning out then overall the tree is healthy and growing.
The hazard of the tree is dependant on the location and the age and if the tree is hollow. Filling the cavity will not help since the fungi sounds like has gotten a good foot hold on the wood. To scrape the decay out you would have to go inside the trunk all the way to the ground which is impossible (similar to filling a tooth with out first grinding out all the rotting places--the decay will continue). The hurricane winds y'all have had the past couple of years weakened the wood surrounding the decaying places and over time the weight of the limb completed the break. You maybe able to cable the limbs to keep them from falling onto the house but more than likely they will keep falling. If the foliage of the tree looks green and full and the tree is wanted I would look at pruning the limbs over the house so they would not fall into the roof. With the conditions you described this may happen again.
Now I have said all this without seeing the location and other factors that can be seen looking at the tree. I would suggest you contact the Florida Division of Forestry a state agency and ask one of their Foresters to take a look. You can call the county forester OR I would suggest you call Ed Barnard in the Gainsville office. He is a Forest Pathologist and can advice you on the best thing for this tree. His contact information is   Forest Pathologist (Diseases)-- Ed Barnard 352/ 372-3505  Ext. 130 email [email protected]
You can tell him I sent you he is a friend and has the same job in Florida I had here in Alabama before I retired.