There are some road front ders from Shimano that can have their return spring crack off, or the tab the spring's end seats against can crack off. But when this happens the der pivots are still freely moving for the range, only the spring's influence on the parallelogram changes. Generally the spring "strength" lessens, not increases...This failure can happen quite suddenly as Al crack growth is fast.

I have seen ft ders frozen by corrosion due to a wet put away and weeks later the next rude. Especially at the end of the season when the winter's first use of road salt was done but the weather turned warm enough for that last ride...

Many frozen ft ders can be made to work by simple hand manipulation. I like to unscrew the limit screws a tad so the parallelogram has more travel range than when in actual use. Then just push and pull the der/cage through that range, over and over and I'll slightly add some off angle force (twist/pry) to get the pivots to have all their surfaces get moving contact to better clean out the corrosion/grime that is in them. I actually find doing this with the der being dry of lube can be quicker than when soaking with oil. Compressed air every so often helps with the cleanup and forcing the following lube into the pivots.

BTW some Shimano ft ders have used a threaded bolt to contain one or more pivots. These can come loose over time and then need retightening. If the pivot is a bolt (shoulder bolt) and if that bolt can be completely unthreaded that would open up the parallelogram/links for even better range and cleaning. Andy.