The 51 ohms you measure across the coil is a good sign - that's the reading I got on one I measured about two years ago. So I wouldn't be suspecting it just yet. Problem is I'm not aware of anyone selling them off the shelf - I looked a while back because my Centaur is missing the factory magnet . Someone fitted a later WMS magnet in mine which is too strong and regularly blew a 3amp slow blow fuse I put on it.
If I remember right:
The magnet has a PTC thermistor in it or something similar - no idea what its value might be.
The gauge on an original Centaur magnet wire I measured was roughly somewhere around 30 or 31AWG - don't quote me on this. There are online calculators to estimate the number of turns. I have to find it again.
If grounding the black-red wire on the magnet works, then go upstream:
* Ground the metal tab of the Q18 driver transistor on the solenoid driver board to manually activate the magnet.
* Further upstream, ground pin 11 of U4 on the solenoid driver board to manually activate the magnet.
If you have no luck when you visit it, post some clear pictures of the magnet showing the screw puncture.