Two things:

1) have no drain on the battery.
Then you did not measure it correctly, you have drain on the battery, the question is, how much? Anything up to 55mA is fine, if you have ZERO, your meter is not connected properly, your meter fuse is blown, you have the leads configured improperly or your meter is bad.

2) Terminal voltage does not tell the entire story. When you place a load on the battery, it's internal resistance comes into play. If your test of the battery is to simply measure the unloaded terminal voltage, you have not actually tested the battery.

Exactly what is the standby current (what you call "parasitic", but there is no such thing as a "parasitic drain")? Storage batteries DO NOT like to be drained slowly over time, they are designed to deliver 200 to as much as 400 amps for a SHORT period ot time. If you have current flowing, it will raise the internal resistance of the battery, such that the load you place on it when the starter solenoid/relay closes, terminal voltage drops, many times, to where the relay drops out. Once it drops out, terminal voltage rises, pulling the relay in, so you get the click-click-click action from the relay.

Of course, you can have a totally good battery but resistance in the positive or ground leads, which gives you the same symptoms. So, have someone turn the key to start and see what your terminal voltage is during that. If terminal voltage stays at 12 or above, you have resistance in the cables somewhere (corrosion, etc.) If terminal voltage falls or jumps around, then the battery is weak, again, probably due to excessive standby drain.