Hi Smii,
Welcome to the Bude & I hope you can understand English.
The Audi S1 is just a simple conversion from GTR2 to GTL and because of this the files that are needed to show the car as a picture or video on the menu screen have not been created and some information is also missing from the 'CAR File' that helps you to see the car in the showroom.
If your game crashes when you try this car it is usually because of an incomplete or corrputed installation. Try installing the car again and do it the easiest way. Put the 'GameData' folder into your GTL folder and when prompted to overwrite press 'Yes To All'. This will not actually overwrite any of your other files or data but only add the data needed for the Audi S1.
With this installation you will still not see the car in the showroom until you go to race or practice, then when you are asked to choose your car you will be able to see it in the showroom only and you will be able to buy it.
If you want to see the car in the 'Dealers' showroom or in your own 'Garage' you can do some very simple changes.
1...Open GTL/GameData/Teams/GTC-TC-76/AudiS1/*File Folders of both cars*
2...Then open the 'CARFile' in each of the folders with 'WordPad' or 'NotePad' and overwrite the line
classes="Full, 2003, SIM_GTC76" with
classes="SIM_FULL, SIM_GTC, SIM_GTC76, SIM_CSL, SIM_TOURING, SIM_NOLONG"
3...Underneath it add the line
Value=1 which means your car will only cost 1 credit!
You should now be able to see the car in the dealers list and showroom and buy it. The only downside of doing this is that the car will be able to enter almost any of your offline races and competitions.
I hope you can understand what I have written. If you need further explanation then please send me a PM (Private Message).
Cheers.
Gee-Deeman
PS. I run a private server for Addon Cars (MODs) for the Bude on Wednesday & Saturday nights if you are interested. See the English Forum 'Sloppy FUN Races':
http://www.altbierbude.de/component/
option,com_fireboard/Itemid,99/func,showcat/
catid,30/lang,en/