5th precept missing from 8fold Path? I can find the first 4 precepts explicitly listed in the 8fold Path- but not the 5th precept regarding intoxicants. Am I missing it in there somewhere? I am wondering if it was a later addition to the tradition.
There is an interesting relationship between the first four precepts and the fifth precept.

For e.g. from the Kalama Sutta (quoted below), we can see that the fifth precept is not included. You can find a similar grouping of the first four precepts in the Sigalovada Sutta as the four vices. It also appears in this way in the Sankha Sutta.

But there's a reason for this. Consuming intoxicating substances is by itself not a vice or evil act (unlike killing, stealing, telling lies and sexual misconduct), but it can cause you to become heedless and violate the first four precepts.

In this sense, the fifth precept is only there to support the first four precepts (and the rest of the training).

From the Kalama Sutta:


  “A greedy individual, overcome by greed, kills living creatures,
  steals, commits adultery, lies, and encourages others to do the same.
  Is that for their lasting harm and suffering?” “Yes, sir.” 
  
  “A hateful individual, overcome by hate, kills living creatures,
  steals, commits adultery, lies, and encourages others to do the same.
  Is that for their lasting harm and suffering?” “Yes, sir.”
  
  “A deluded individual, overcome by delusion, kills living creatures,
  steals, commits adultery, lies, and encourages others to do the same.
  Is that for their lasting harm and suffering?” “Yes, sir.”


From the Sikkha-Dubbalya Sutta:


  "Monks, these five are things that weaken the training. Which five?
  The taking of life, stealing, sexual misconduct, the telling of lies,
  and distilled &amp; fermented beverages that are a cause for heedlessness.
  These five are things that weaken the training.


Please see this question for more info on heedfulness (appamāda).