No fluid lasts a lifetime. These "maintenance free" units were a sales pitch to new car buyers and a way for VW to save a few bucks, while forcing owners to go to a dealership or reputable VW mechanic for eventual service. I did the fluid and filter twice on my 2000 Jetta before I sold it with 175K on the clock. It's a bitch, but not impossible. There are some good DIYs here. When it comes time to refill the fluid, I'd recommend measuring how much comes out (by putting it in a gallon jug, etc), putting the same amount of new fluid back in, plus maybe a touch more (to compensate for any that may have evaporated, etc). If the gears are slow to engage when it gets cold, you probably didn't put quite enough in.I also have an 2004, 2.0L jetta automatic. Do these cars need their transmission fluid ever replaced? I thought these were "lifetime" but have also heard that that word lifetime is misleading, and often it may be wise to replace the fluid.
If you know someone with that expensive @SS VAGCOM software, you can do it the recommended way, but who has that kind of cash? The one thing you DEFINITELY don't want to do is to take it to a garage that either doesn't know what they're doing or are trying to cut corners. These shops will elect not to drop the pan, drain the fluid, and replace the filter and gasket. They will instead hook up a pressurized line, flush most of the old fluid out, put new in and call it a day. All this does is stir any metal filings from normal wear and tear up INTO the transmission where it doesn't belong and burn it up shortly thereafter. When these cars where relatively new, there was story after story of this being done and owners having their trans burn up after just 60-70,000 miles. Long story short, do your research and take it to someone you trust. Or, do a little more research and tackle it yourself. Just be sure to get the right fluids/parts and triple check your work.