I heard it can't be older than 8 years, or is this only true if I want to import permanently?
7, and yes. Cannot be diesel
I haven't bought a car yet
So let's say I get the car to Lebanon tax free because of temporary import and it breaks down after a year.
Don't buy a car that will break in a year then?
just trash it or do I need to pay the taxes then since the car hasn't left the country
Both, you answered your own question. The car hasn't left Lebanon.
Any idea where I can get all the papers for importing my car?
You need to be sure, right from the beginning, if you are buying a car for Lebanon to keep there and move there (which you probably will do, if you survive a year) and then MAYBE bring it back to Germany, or if you are categorically against living in Lebanon and will be there for no more than 12 months.
If you decide to buy a car in Germany, you will pay VAT there, which is something like 21% of the cars value, plus, in Lebanon if you decide to register it there and settle down, it will cost around 50%. Now, if you own it in Lebanon for 6 months and have driven it for 5000km, you can bring it back to Germany tax-free, but, if you own it in Germany, and then wish to bring it to Lebanon, you will have to pay VAT twice.
Just get the papers from the German side, you need a certificate of "touristic or temporary export" plus ask for "bara2it zemme" paper from the same source
No such papers exist here. We live in free countries. You need just your certificate of registration... which you won't have, unless you register the car and pay taxes in Germany. You need to understand also, @AW888 - I would recommend that you buy a new car from a Lebanese dealership. Then the car will be service-able and repairable under warranty both in Lebanon, and in Germany. This is because official dealerships have international warranty. They may chose not to service your car if you bought it elsewhere, therefore, go to official places (and they probably have connections in the customs who can reduce the value of the car, saving you money on import taxes).
If you get a European spec car made in Germany, you can chose to get export plates. You may be able to drive around Lebanon with these plates without paying taxes, but seeing as they are issued for a few weeks, the plates will be expired when you enter Europe, so you will have to pay taxes in the end. If you contact dealerships in Dubai (which sell US spec vehicles, mostly), you can get cheaper cars, tax-free (and you can refund the 5% import duty when you bring the car out) sent to Lebanon for $1000 as @METNI said... but when you return to Europe, you will need to spend $$$ on re-certifying the car so taht it meets European requirements (which may cost a couple thousand Euros). Had you lived in England, I could source you the European headlights that you needed so that you could get it inspected, and once you'd pass the test, I could take the European lights from you and you could put the American ones back in, but in Germany, the system is way more complicated.
Message me and I can find you the car that you need for cheaper, and can find you people that will get it into Lebanon for you.