Nice job! I admire that you went ahead and fixed it up, despite the discouragement. To my mind, fixing up old bikes most people don't appreciate is always a good thing.
Simplex front derailleurs worked perfectly well BITD,
if they were properly set up and adjusted. Most were not. The acetal resin does eventually degrade and most will crack eventually - but remember they are many decades old now. FWIW I don't recall seeing any broken ones until sometime in the 90s.