The plastic parts of those Futaba radios are made of low quality. I have seen many of them crack in different areas, and you must be the double of careful because if your radio falls from your hands it will be broken for sure. Before replacing the spring take a second or third look at your radio and see if there are plastic parts missing or broken.
Tower radios are a copy of Futaba so you have to expect the same or lower quality.
I would buy other brand, I highly recommend the JR radios, but there are other brands in the market like Hitec and Airtronics but I can't tell nothing good or bad about them as I hardly have seen them (JR and Futaba seems to be more popular at my field).