First Time Kegger Question

I had a leak somewhere and drained all my CO2. I'm planning on replacing all the O-rings and then trying to find any leak that may remain. I have another keg with a different style lid and posts. I was thinking I might just put new rings on the other lid and posts and use them to make things a little easier. Are lids/posts basically interchangeable?

nope, some posts are not even interchangeable on the same keg

I have found the following info someplace on the web, can't vouch for its accuracy

Firestone V Challenger, Firestone VI Challenger, Firestone Super Challenger
Gas 9/16"-18
Liquid 5/8" -18

Cornelius Spartan & Super Champion
Gas 19/32" - 18
Liquid 19/32" - 18

Cornelius R (pin lock)
Gas 19/32" - 18 (2-pin)
Liquid 19/32" - 18 (3-pin)

John Wood 85, Firestone Challenger
Gas 11/16" - 18
Liquid 3/4" - 18

Firestone A, Firestone R, John Wood RA, John Wood RC (pin lock)
Gas 9/16" - 18 (2-pin)
Liquid 9/16" - 18 (3-pin)

Are you sure that's where your leak is from? When I got my set up this summer, I had a leak too. Mine was from the gas line, the SS coupler on the gas line just needed to be tightened. I noticed a lot of hissing, hit everything with starsan to find the point of gas loss. Took a screwdriver and 3 seconds to fix that problem. Might want to check that out before you potentially throw away good seals.

I agree with Crinkle. You sure it's the keg? Mine leaked cause I didn't have the regulator tight enough on the CO2 tank. You can typically hear a leak when it's present.

increasing pressure will turn a slow leak into a fast leak, which makes it easier to find

do you have your nylon washer between your regulator and the tank?