I am the previous owner and I am horribly fastideous! Thats why I spent £3000 on a rebuild! Checking the oil on an XT600 is an art form in itself. After the rebuild Dave Lambeth took 25 mins explaining the technique for doing this and demo'ing it.
1. Run the bike for 10 mins on the road to fully warm up the bike and engine. (this also sucks up all the oil from the crankcase where it can drop down to if the valve in the oil line is faulty) ( if it is there are no probs, just wait before checking the oil!).
2. Bring the bike to a stop but do NOT stop the engine and either get a mate to hold it upright, or prop it against a wall, do NOT put it on the side stand( you need to do this beacuse the oil pick up is on the right side of the bike).
3. With your third hand take off the side panel and loosen the oil filler cap to check the oil being aware that it could spurt out everywhere!
Yep, I know it sounds mad. Thats what DL said and that's what I fastideously did every 200 miles across the desert and back.
The oil level didnt drop through three changes and I would be rather suprised if it had since my last check 200 miles ago!
If you need to know stuff just give me a call!!