Edit:
I resolved the issue.
Sterling appeared in the Command Center at Forlorn after about 4 in-game days.

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I am sure i messed this up (searching in these forums didnt provide answers i was looking for).
I didnt go through all the dialogues with Sterling.
I completed "three card bounty" and "i dont hurt anymore".
I only see Betsy and Bitter Root in the Barracks at Forlorn, Sterling is no where at Mc Carran or Forlon, i have exhausted all possibilities, searched everywhere at every NCR model, it looks like Sterling virtually disappeared.
Either way, it appears from what i have read on the internet, that even if i do fine Sterling, i wont be able to get any dialogue anyway.
I suppose the Full Maint Perk for Raul is squelched at this point, only way is to go to a prior save.
If you have a suggestion that might help, please post.
Thanks.
Edit:
Google searching seems to indicate that if Sterling is not at Forlorn, he may have been killed walking from Mc Carran to Forlorn, just wonderful if thats the case.
Oh well.