It is beneath the LCD of the camera. It isn't difficult to get to it. Only a few screws to remove. Remove the winder lever then remove the right top cover. This can be seen on the P67-II service manual page 5 and 6. Then unscrew and lift up the LCD module (just get it out of the way for seeing the shutter magnet). You can re-attach the winder lever without the right top cover. If the winder is stuck you can use a pin to nudge the winder locking mechanism to release it. Very easy to do, no forcing anything. Just a very gentle push. You can then wind again. With the LCD module out of the way (cable to the LCD still connected) use a small syringe to drop a tiny drop of ISO Alcohol to the shutter magnet. The syringe needle does not need to touch anything. It will clean up the magnet and not sticky any more. It will again release the winder lock each time when the shutter is fired. You can observe how the lock is released by the lever moved by the shutter magnet causing the winder lock released. You will also realize how well the winder is built. You will believe it is a fairly durable winder.
I drilled a tiny hole on the back of the right top cover (black plastic). The hole is tiny. I can stick a pin into it to nudge the locking mechanism in case the shutter mechanism becomes sticky and fails to release the winder lock again. The pin is to nudge the winder locking mechanism, not the shutter magnet. Never mess with the shutter magnet. It has been 20 years since then. The winder has had zero occurrence of getting stuck again.