BmB said:
The problem is if Vader had found Obi-Wan he'd prolly have tried to take revenge on him no?
Not necessarily.
First of all, as I said above, if Vader cares about his son's welfare — which, despite being a Sith Lord, I believe he does — there is some value to letting Obi-Wan live.
Second of all, how much more revenge does he need? The Jedi have been wiped out. Vader himself personally slaughtered all the younglings at the temple, and Obi-Wan was no doubt close to many of them. The once great Jedi Master is now damned to live out the rest of his life as a sad old hermit on this pathetic rock called Tattooine. Isn't that enough?