I can’t see what is embossed on the seal – is it the Mercury logo? Generic lead seals are available and can just be shut with pliers or with a custom seal, like Merc used. I have used generic seals to reseal motors I rebuilt, just with pliers.
If the motor has good compression and turns smoothly, I would fix the ignition and run it. See how it sounds, etc, at low revs. Those motors are hard to wear out if lubed and cooled correctly. 😉