All 1200GS finaldrives have a drainplug. It was placed at the 9:00 o'clock position to facilitate greasing the driveshaft at time of service. Yes, BMW first stated that the final drive had oil-for-life, and i'm sure they were quite happy with themselves when they realized this was a bad idea and fortunately placed a drain plug in the 9:00 o'clock position...just in case This is indeed a drainplug for it serves no other purpos.
The final drive also has a fill plug located on the hole containing the speedo sensor. All new final drives like Alli Baba pointed out have the drainplug re-located to the bottom of the drive, and a fill plug located next to the speedo sensor. Personally, i find no reason for this. If you need to change the fluid in the final drive, you would think it's time to grease the splines at the same time, a much more urgent job, therefor the 9:00 o'clock position makes sense. Also, the new fill hole is no better than the old one, and you need to remove the speedo sensor anyways to check the magnet for evidence of pre-mature wear. It's all just more work to do the same job IMHO.
Having said all this, i really like the sleek system for maintinence BMW has come up with. Basicly, you remove the brake caliper and rear fender, pull the plug (wait for it to drain if it's at the bottom) pull the paralever bolt and let the drive tilt down. The entire driveshaft pulls out for maintinence. No more stretch bolts, no more breaking the lock-tite held pivot bolt or removing the rear shock on the R100. Basicly, a really sleek system, all done in under an hour. As far as reliability goes, the final drive would be the last of my conserns. I would be more concerned about leaking output seals on early models, spare antenna ring, warped rotors and the fact that there is no serviceable fuel filter, the later which hasn't resulted in any problems that i have heard of yet, but sounds strange to me all the same. Truth is, as Margus has pointed out, over 100,000 of these bikes have been sold in a short period of time. Although the problems we hear of are a small percentage, they have a very loud voice.

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