The flaw in your reasoning is that just because there isn't any evidence there's damage from liquid on your hardware currently, that doesn't mean the damage wasn't done by it. Ever hear of Occam's Razor? The simplest and most straightforward explanation is usually the correct one. You as a medical student should know and understand this better than other people, unless you haven't studied pathophysiology yet.
Right now you only sound like someone looking to take advantage of an AppleCare warranty repair when you clearly aren't entitled to one.
That was a nice long rant, but regardless you can't prove a negative. You can't prove that damage wasn't done. What I've been saying in this thread is that Applecare needs some standards. If they claimed it didn't go past the keyboard when it was opened, then denial of warranty on this is a bad move. They charge a premium for it. It should be in the customer's favor unless they can prove abuse, and they need to set standards beyond the arbitrary judgement of one employee versus another.
The other thing is that the repair fees are out of line especially when they aren't fully testing the machine. They're just saying give us $800 and we'll make it work eventually. The logic board was never confirmed to be bad through any testing up to this point, and $800 is much more than a diagnostic fee. Some of the local authorized repair shops charge fees as high as $90 for diagnostics which is then discounted from the price of the repair if you choose to go ahead with it, and their service is on par with Apple. I'm sure you've read complaints on here before where someone took their computer in, logic board was replaced, and they were still having issues after the fact.
DO NOT SEND IT IN TO APPLE!
Do you have access to any spare 2.5" HDD's? I highly suggest popping in a blank drive, and installing OSX from scratch. It's very possible the lag is due to a dying HDD, which got wet. Typically when a motherboard gets wet, it either works, or it doesn't. You wouldn't notice a slow-down in speed.
If it is in fact a damage hard drive, you would be correct. I mentioned to look at activity monitor when this happens for what is going on with the cpu, hard drive, etc. The Apple employee stating give it more ram when this was a recent change just shows a lack of competence. I'm still in favor of having it looked at by a local authorized repair center where you can actually talk directly to a technician.
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