I have 3 Shimano Sahara 750’s - they are used for crappie and small creek fishing. Mine are at least 20 years old. Reels are still in great shape but recently 2 of them started displaying a problem with the bail not fully closing. I manually close them by hand, usually all it takes is a light bump on the bail and it snaps down. But mine are not closing the last 10 to 15%. I made sure they were clean and oiled things but they are still doing it.

 

Is it a common thing for bail springs to go weak? Maybe I can order replacements.

Shimano doesn’t use the old twist springs. Their coil springs don’t weaken that I’ve seen. What’s actually happening is the bail wire is slightly deformed and binding the hinges. Gently squeeze or pull the side of the bail and you’ll see the hinges free up. 

Probably been dropped and the bail bent.  Like DVT said try and bend it to get the hinges free.