I wouldn't worry about leaking kegs until you get some pressure put on them. Remember, these things have been in service for a long time. Another thing you should do is get a couple of o-ring kits for them. There are 5 o-rings that will dry out over time. They need to be replaced every couple of years. Most people selling kegs will have reconditioned them i.e. they are clean and have new o-rings installed.