I'd be curious to learn your formula for puncturing your can lids. I used homade metal pail feeders back in the late 70's when I kept bees for about 6 years and never had a problem with them. Now I am stymied; all of my experiments with making a pail feeder this season (all plastic) failed, never achieved a proper vacuum. They dripped too much or not at all creating too much vacuum. So...I ended up buying one which works fine.
The problem with the plastic is, when it gets cooler and warmer the plastic moves with the expantion and contraction and so squeezes out the liquid. That is why most people use glass jars for homemade feeders.