can't see ish from that picture, but i have the same problem on the one mango tree that i inherited with the property. I think it's a madame francis (although if my memory serves me correctly, some of the fruit last summer was noticeably less fibrous than others--if that's even possible). I cut it back pretty good last summer, and it oozes orange sap from several places on the trunk, and has been oozing for 6-8 months now, though the rest of the tree seems to be thriving. It didn't set any fruit this year but I expected half as much when I chopped it back. I still need to chop back the other of the two main trunks.
Is the tree sick, or does this normally occur when pruning a mango heavily?