I was in Germany (Ramstein) for 3 years (2003-2006). I purchased my first VW while I was there. I bought a 1986 1200cc gas engine Golf. The car was great. I bought it on ebay for 300 Euros and drove it for 3 years. When I got back to the states I bought a 2004 Jetta TDI because I loved my German spec Golf so much. I suggest you take your VW with you. Parts there are cheap and you have PLENTY of good mechanics there that can help you out. Or you could go there and buy a brand new VW with American specs and ship it back to the states for free when you PCS. This can save you lots of money when buy a new car there but it really depends on the Euro/Dollar rate because if I remember right you have to pay Euros for the car.
Things to know about the TUV inspection that you will have to do:
-The Germans are big on cars, and they want them to be safe. All safety features must work on the vehicle.
-Tires are one of the biggest features they look for. The tires must have the right amount of tread (sorry I can't remember the amount) and must be matching tires. In other words, you must have the same size and brand tires on each wheel.
-Brakes are tested to make sure you have good stopping power
-Car in Germany WILL rust. They will make sure there is not too much rust on the vehicle
-Exhaust must be within the limits (again, don't know what they are, but your US diesel specs should be well within the euro-specs
-Diesel is (or at least when I was there) MUCH cheaper than gas off base, but not all the bases sell diesel. This may mean you have to buy gas stamps
-Diesel is best for raod trips, so your diesel is a great choice. I filled up in France once and paid 80 Euro to fill my Golf and buy a liter of oil
The German inspection is tough, but the American inspection is a little easier.
If you wanted to make some money when you PCS and not take your car, you should buy a truck to ship over there with you. Small trucks such as a Ranger extended cabs sell for a couple of thousand dollars more there than they do here. You can PCS with a used truck you buy for 3-4K on CraigsList and sell it for 5-6K on base in Germany. Trucks are in low supply and high demand there. Then, if you don't bring back a brand new VW, consider bringing back a Volvo C303 or other vehcile that you can buy pretty easily and cheaply over there and sell it in the states. I made about $5,000 on a C303 I bought in Sweeden and had shipped back for free. You just have to make sure it is old enough that it doesn't have to meet the US regulations when it gets to the states or you'll be paying for it.
I hope all this helps you, and I hope you enjoy Ramstein as much as I did. If you get a nice car while you're there then you should take advantage of all the places you can easily drive to. It only takes about 3-4 hours to get to Paris and you can be all the way to the Czec Republic in about 6-8 hours. The country is beautiful and I'm certain you will enjoy all that it has to offer.