...liquid vitamins that arrived with seal securely intact,but screw cap cracked?
This arrived in post...glass bottle packaged only in a SealedAir bag.
Am I worrying too much?
I presume that you are using them as a supplement and not therapeutically, as a treatment for a diseased process.
Not that it makes much difference to my answer ;-)
They have been hermetically sealed at the factory following autoclaving and even with the cap cracked/ broken, but seal intact, they will not have lost their potency or invited germs.