I'd be careful about the video linked in post #19, the Seiko shutters
do not have a permanent magnet component. The part that the video calls a "magnet" is the Anvil, and is not a magnet, just ferromagnetic steel. Over the course of use, it may become mildly magnetic, but it's function is not to be magnetic. It just closes the magnetic loop when the coil is energized. If anything, it may need a degaussing.
The electro-magnetic switch on these shutters is not technically solenoid (which has a moving rod pulled by the coil, as shown by koraks), it's a horseshoe-anvil release. None of the parts are permanent magnets (neither are any parts of a solenoid). Note that later electromagnetic releases did use a permanent magnet (Hasselblad, Nikon, Canon, Pentax, etc...) but that design came later, associated with the development of neodymium magnets.
In the Seiko shutters, the horseshoe component becomes an electro magnet when the coil is energized, attracting the anvil to the ends, the linkage from the anvil prevents the shutter from closing. Releasing the Anvil allows the associated linkage to release the shutter, which then closes. The Anvil only moves ~1mm.
View attachment 362316
The coil is on one leg of the horseshoe, and the anvil pivots on a linkage to the pin to it's left, which is linked to the lower arm in the photo, which holds the shutter open.
The coil rarely breaks, and is easy to test with a meter. The usual issues are with old lube on the linkage, making it stiff, or a failure in an electrical components resulting in low current to the coil. In the latter, the shutter dose not work for longer times, as the Anvil is not held against the horseshoe properly.
If the shutter is not closing, then the Anvil is not releasing from the horseshoe, which can be caused but stiffness in the linkage, or a combination of that and the horseshoe and anvil retaining some magnetism, so there is a weak force holding it together. Cleaning the linkage, and degaussing the Anvil and horseshoe would help (although degaussing is usually not necessary).
The other thing to look at is oil on the shutter blades (especially near the pivots where you cannot see it), this causes the shutter to stick when open. This is more common on mechanically times shutters, as they have a lot more lube in the area. The shutter blades, pivots, and associated components are designed to run dry.