MacBook Pro Retina(Mid 2014) crashes - Apple couldnt find the problem

My MacBook (MacBook Pro 15" Retina Display Mid 2014) crashes after ca. 2 hours. After the first crash, it keeps crashing more and more frequently. Next day I can use it again for 2 hours, initially.

I ran a system diagnose which didn't find anything and reinstalled OS three times. The problem is still there. Then I brought it to an Apple Reseller and Repair Shop (Gravis). They also couldn't find the root of the problem and suggested to replace the logic board. As the warranty ended a few months ago, this would've costed 700€, so I decided against it for now and look for the solution myself.

I'm very disappointed in the value I got out of this very expensive Laptop and I'm hoping some one has some experience with this kind of problem.

Thank you!

@mayer I couldn't find anything about a "Flat Rate Repair" in Germany but thanks!

@reece and @vmonteil I opened it up got all the dust out (it was quite a lot) and looked for the above described indicators for water damage (but couldn't find any). And low and behold, I can use my computer for around 5 hours now, lets see if this was indeed the solution.

For anyone with a similar problem:

- you will need to buy a Pentalope screwdriver and another one (I forgot the name) , which are almost comically expensive (15€),

- watch a youtube video about how to open and clean MacBook proberly and go for it! Its not that hard, don't use water, etc.,

- but be careful about all the parts and especially the little screws,

- this might cause an insurance problem, so check that first.

Thanks again!

@vmonteil: I did not remove the dust from inside yet. Could that really be the issue?

I will try that though thanks!