I've never had leaking from the bottle or the seal of the nipple. If my daughter leaves it tipped over it may leak from the nipple hole (we are using level 2 nipples). That seems normal, so I can't complain.
I've never had this problem - I did find that if the milk was hotter, it sometimes would squirt out of the bottle. Also make sure you have the right kind of nipples for your son (1 being the smallest and slowest flow - 3 being the fastest flow)