The vent is there for reasons as the name implies. It's a safety feature to prevent the cap from exploding if over-tasked. Yes, without the relief on the end, the caps have a potential to become missiles when they go. I had one go off when my hand was over it. If you ever had a fire cracker go off in your hand, the feeling is quite similar.
For reasons for the leakage, I would look at your design, primarily the layout of your pcb. If you are experiencing per-mature failures on your electrolytic caps, this may be do to high operating temps on your power supply. Are the caps in close proximity to heat sinks? High temps will dry out the electrolyte in the caps preventing the caps from holding a charge, thereby preventing a lot of ripple.
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