Imagine an alien race. They are the creators of Unspecified Advanced Alien Technology™. One day they lose one of their ships. The crew had to evacuate, and the ship kind of crashed on a random planet. About four thousand years later, humans found that crash site, and found a few artifacts that they managed to reverse-engineer.
These artifact are: a FTL drive core and an artificial gravity generator core. Those are the only two things that need to survive. They may be encased in a box, they may be made of indestructibium, whatever. What matters is that they survived against the elements.
How are these devices functioning in the first place? Unspecified Advanced Alien Technology™. Essentially you have a core. You feed that core some electricity and a signal, and then it does stuff based on the signal.
How did the ship survive the crash? By using some sort of foam-airbag-thingy. The ship was engulfed in that, which allowed it to survive entry and the crash. Then the thingy degraded, so it couldn't have protected the ship for very long.
Are the devices functional? Not really. There are in one piece, give or take a few bumps. They were in a good enough condition that they were taken apart, studied and copied; but not in a good enough condition to be working.
The question is:
What kind of materials could survive for that long unattended?
We assume nothing was destroyed by the impact, however since then a lot of stuff has stopped functioning. We'll limit to materials that exist on Earth, or materials that can be manufactured using materials that exist on Earth. The fancier the materials, the better. I'm looking for a few types of materials that could be reasonably used in complex machinery/electronics.
If your answer is none, then what kind of materials would survive the longest, and for how long?
As a bonus question:
Where should the ship crash in order to be buried?
The burial can take anywhere between 0 and 4000 years, but it has to be completely buried. The ship is the size of an attack submarine. I'm looking for biomes in general, not specific world locations. Bonus points if you can tell how deep it'll be buried. You can also take location into account when answering the main question.