leaking wet suit

That's why it's called a wetsuit (as opposed to a dry suit, which stays dry - hopefully- on the inside)

Yes. It is a wetsuit, you get wet wearing it. If you dont want to be wet, get a dry suit, but you cant really swim in one of those. The wetsuit is there for insulation and somewhat for bouoncy and hydrodynamics.

Wetsuits allow water in so that your body heat warms up the small layer of water between your skin and the wetsuit itself.

As long as it is still tight and not carrying around large amount of water.  I rented a suit that was too big for a race and although it did keep me afloat.. I know I was taking a few gallons of water with me where ever I went ie slowing me down a bit.  When you get out of the ocean, pool  etc, HOW MUCH WATER DRAINS AWAY? Does it feel like a "flush".   It should not drain too much if it were tight in all the right places.
I now have a suit my kids love.  I open the neck to allow water in and then let go.  The compression of the suit makes a water fountain up my neck.  They think it is hilarious.  That is a tight suit with no extra water.

You're gonna be wet but you shouldn't feel water flowing through or sloshing around (like I did in my first wetsuit); if you do, it's too large.

Water should not go in throught the neck.  May be it's getting in from the "mesh" material area like the torso or under arm and where the zipper is.  A wetsuit is NOT waterproof.  It is a device to keep you warm in the water by trapping a layer of water which is to be warmed up by your body temperature.  So initially it would be cold. 

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