Or much more likely, the grease in the mechanism that trips the second curtain has dried out, making it sticky, or there is corrosion causing stickiness, or foam has gone gooey and caused the shutter curtain to become sticky.
Magnets don't "wear out" in my experience, and springs don't generally wear out either. Grease dries out quite often. Things corrode and jam. Foam deteriorates and turns into a gooey mess that clogs mechanisms.
All of these can be easily fixed by cleaning, lubricating, and adjustment.
Of course the actual cause of your issues won't be found through speculation - it'll be found by someone who knows what they're doing actually taking a look. And from the sound of it, the "repair man" you spoke to isn't one of those people.