MacBook Pro (mid-2009) is a complete mess: constant freezing/crashing

Question

Let me start with a bit of history: I bought my MBP in August 2009, and since then it has gotten progressively more aggravating. The hard drive failed a year ago and I had it replaced in April, and then it failed once again, and got a new one in October (2010), along with a new hard drive cable.
Unfortunately, about two weeks ago, the computer went completely on the fritz. It would freeze (beachball) for no apparent reason, other than when the hard drive was being used, such as going through iTunes, Safari, or Aperture. However, after doing a disk check, both in Disk Utility and using fsck in Single User mode, there were absolutely no errors to be found, which, unlike the two times my hard drive failed, shows that the HDD is indeed okay.
I did an archive and install and it seemed to have helped the problem for a grand total of 2 weeks. This week, my computer starting going at it again, and not even consistently. On Tuesday, it would be just about unusable, beachballing at the slightest "load" (such as opening a third tab in Safari), and that one freeze would bring down the entire system. Everything, even if it's working, is slow and laggy--things like scrolling down or clicking on something might trigger a beachball for a second or two, or just take far too long even with no beachball. After a bunch of forced restarts, my screen began flickering on the edges, most visibly at a high brightness. However, after several more restarts, it quit doing it--this also happened during the first set of crashes two weeks ago.
Yesterday, my computer was more or less fine, and I might've only restarted it once or twice. Today however, we're back to where we were two days ago--constant freezes that all but prohibit me from even going on the internet. The computer gets stuck going to sleep and has trouble waking up. It doesn't respond fully to when I plug it into my Henge Dock (the Henge Dock is not the problem, because the MacBook acts just as badly on its own), in that the display never shows up. One time today, it woke up from sleep, but the menubar icons (SystemUI Server) had crashed, and subsequently everything else as well.
The most confusing part about all this is that there is NOTHING to be seen in Console in terms of any crashes, whether an app, the kernel, or any processes. I also took my computer to the Apple Store this week, and Spotlight didn't work except for maybe a dictionary entry on the term entered (I don't use Spotlight so I never noticed this). Even when booted off an external HDD, that external OS couldn't search my hard drive either, or it was really, really slow at it. More surprising were the results of the hardware test; it came up completely clear, with no errors. The genius suggested I do a clean install of my OS, which is a ridiculous solution, as I had done this last year already and the OS I was running before had been migrated from multiple computers for years beforehand. I'm sure you all well know how big of a pain it is to do that. Otherwise, it's sending the computer over to the Apple depot.
I'm sorry for the extremely long-winded rant/problem descriptions, but I really just want to know from people with perhaps more experience in incomprehensible Mac problems what might be wrong with my computer. I really think it's a deep hardware issue, such as a bad logic board. I'd like to hear some opinions before I back everything off and ship this POS (the most unreliable Mac I've ever owned) to Apple. Thanks so much for reading and I hope somebody can help answer my question!

Answer 1

After opening the computer up the only evidence of where liquid has been is on the corner with hard drive / cd drive etc. There is not evidence of liquid damage to logic board on the otherside of the computer. Hard Drive and Ram have both been replaced.
Obviously there is still a chance liquid has got to the other area and I have not realised it...