Yeah sounds like you must've got the culprit.
I just got my Macbook Pro back today after about a month and half of not working. It would usually randomly just not boot and than if it did boot it would freeze after about 10 mins so Apple got a good series of calls from me with no resolution other than driving to 45 mins away.
After doing that 4 times they finally replaced my harddrive which didn't do shit. So I brought it to a local computer shop who were resellers and they just said hell with it and gave me a new logic board.
Seems to be going well now. All without spending a dime. Stoked on that.
Sorry for going off there.