Good catch!
Obviously this anaerobic corrosion where the hose was slid over the tube, definitely something to be on the lookout for. I can imagine a slow leak at first without much indication except a bilge pump running occasionally then a more constant bilge pump, then a constant stream. I can't see where this would be catastrophic unless you did not heed the warning signs, then your bilge pump would fail when you're not aboard..............glug, glug, glug.
Think there's enough room to use a tubing cutter to trim off the corroded part then use a longer hose? I'm thinking of a repair without removal of the mast. Think you could fish the tube through the slot where the pennant leaves the mast? Maybe? Obviously, the boat would have to be on the hard, but I don't want to remove the mast if I can help it. Just thinking out loud.