Joanne - Obviously the tree was damaged at some point which would allow disease to enter the tree. Check out this website to see if any of the listed diseases fit your tree. Take special notice of Bleeding Canker as this looks like what it may be.
Rod, I've lived with that tree for over 30 years... there was never any damage. For the past few years, the bark has been getting whitish, the bark sloughs off and that bumpy growth looking stuff shows under where the bark sloughs off.
I certainly will have a look through the information you've suggested and thank you very much for your response.
That tree lives very near the back of the house, is thick through the trunk and tall; I'm afraid we might have to take it down... if so, it will be sorely missed.
I think this will help