I recently purchased a used mim strat in pretty good shape, but I am getting a buzzing from the open G string and also when G string is fretted pretty much anywhere on the neck and also from the D string only when fretted from about the 9th fret to the bottom of the neck. I also noticed after lowering the action to about 4/64 there is fret buzz on the low E string (thick E string) from about the 12th fret down. The neck looks pretty straight and everything seems tight. I have noticed that if put slight pressure over the g string where it lays in the nut the buzz on the open g seems to go away. Also the buzz was there on the g and d before I lowered the action. Any advise would be appreciated

First and foremost, buy a good straight edge, and a set of feeler gauges. Then use the info in your owners manual, or on this site, to measure the relief in your neck. There should be a slight amount of bow, meaning the neck should be curving under string tension. A trained eye can get close without measuring, but you should set it up right. A good setup may solve all of your problems. I've seen neck relief issues cause open notes to buzz in the nut. Once the guitar is setup, if it still buzzes on open notes, your nut is getting too low, allowing the strings to buzz on the first couple of frets. A new nut, and MAYBE a fret level and dress will have your axe playing so good you won't believe it! Don't panic, your guitar's issues should be an easy, simple fix.

Thanks, it does look pretty straight with a slight amount of relief but I will try the straight edge. The other thing I meant to mention was that when I tried to set the intonation every string was right on except the low E string and I could not get the intonation right on that one no matter what I did.

Well, for the intonation problem, you COULD have too much relief, but your relief would have to be really excessive. IF nothing else works, take the saddle off and remove the spring from the adjustment screw, then reassemble. That can give you another 1/8 inch or so of adjustment. Also check to make sure your bridge isn't raised more than about 1/8 inch from the body. Check the relief and the bridge rise first, before you remove the spring, cause they may fix you right up.