i bought used cornie kegs and they were under pressure when i recieved them...cleaned them up installed new o rings except for the lid...and the lid leaks a little with the soapy water test at 10 psi..and it leaks pretty good at 5 psi...at 20 it doesn't leak at all i am useing lube on the o ring....the o ring is like new what pressure should i be running to serve my beer maybe i need to tighten the clamp?....or should i just run the pressure high...