$402 for a 6K doesn't seem excessive, especially with a final drive fluid change. Here's a few points for consideration:
-BMW Super Synthetic Oil is like $15 per quart - your machine takes 4 quarts, for $60.
-FD Fluid is almost $20 per quart. The FD only takes about 230ml, but you're still going to be charged for a quart. Incidentally, this is a -really- easy DIY service for the future.
-The BMW OEM oil filter costs about $20.
-Adjusting the valves requires stripping off some of the lower tupperware, which involves removing the left side wing cover, the crash bar, and all of the fasteners on the lower plastic.
Just from the parts tally, you're already looking at north of $100, plus incidental parts (crush washers, etc). Most BMW shops are right around $89 per hour for labor, so your tally of $402 is probably $100-150 parts, 2.5-3 hours labor, and some tax. Spendy, but not ridiculous for what it is.
Of course, for well under $400, you can buy a Clymer's manual, some tools, and all of the consumables for the 6K service. Once you have the proper tools, the future 6k's just require time and consumables. I'd guess you'll routinely get away for $100-120 per 6K if you did your own. Just food for thought, as the longer you own your LT, the more "worthwhile" it might be to discover your hidden mechanical talents