If my memory serves me well, the 2002 model year of this bike was a single spark cylinder head which was prone to low speed surging due to a very lean fuel mixture. In 2003 they switched to a dual spark which fixed 90 % of the tangible problem. My 2002 1150RT surged like crazy until I added a Techlusion fueling middle which takes about 10 mins to install, and instantly fixed the problem, and the bike ran much smoother. It had 36K on the clock when I bought it - one owner bike. Other than that, the starter needed to be pulled an lubed (gets a bit sticky with age, and can sound like its grinding on start) Easy fix The rear shock oil reservoir also needed to be refilled (another easy fix) and a the bike you're looking at will likely need it as well. I pulled the throttle bodies and cleaned them out (the were full of junk)
The servo brakes take some getting used to (very touchy) but work great. Make sure that the fluid has been changed out - these needed a special flush procedure, and I believe that the 36K mile service also calls for a new alternator belt.
There is the final drive issue, but in reality from what I have read the vast majority of these bikes had no final drive problems. I loved that RT, it was a great looking, great all round bike. Despite the fact it was 10 years old the shape still looked relevant. There is a TON of info online at BMWSPORTTOURING.COM - helpful people with years of experience with this bike.