Do you have coke kegs? They have the little pins on the sides of the connectors. I've found they don't quite seal right unless you have lots of pressure on them. You should just have to replace the spring valves (2) on each keg and all of the associated O-rings.. (I think about 5, including the big one). If it continues to leak, the keg may have been physically damaged or altered in some way. People come and go in this hobby, and you can occasionally find deals through CL, ebay, and even local homebrewing clubs on used gear.