There are two types of wiper mechanisms. The earlier type has metal rods driving gearboxes behind the wiper posts, and those have a lot of potential to develop slop and not park fully down. The later type has a cable drive and is much less likely to get sloppy. I would expect a '67 to have the cable type, but can't say that your particular car does.

If there is slop, you can easily determine that just by moving the wiper arms by hand. If it's easy to do, you have slop and that's the likely cause of the problem. If not, it probably is an electrical adjustment, but that goes beyond what I know how to do.