Just thought I'd share a little issue I had and what I ended up doing to resolve it regarding leaking oil feed lines (2001 ES Bullet) at the head and engine case. Some may be well aware of these type issues, others maybe not. There seemed to always be some weeping at the head connections, and a little dribble at the bottom engine line connection. Things became worse after having fiddled about with the lines when I was trying to make sure there was oil being delivered to the head. Ended up stripping the threads in one hole after attempting to snug up the banjo bolt.
So after inspecting things I discovered that the real culprit is that the banjo bolt threads are not long enough, part of the bolt body protrudes and obviously bottoms into the head and give a false sense of snugging up. The lines would still rotate slightly when tightened and any further tightening and the thread would be pulled out/stripped in the head. The head oil line bores have threads much deeper than the oem banjo bolts engage, the drilled oil feed passages are at the very end so a longer bolt will work to solve having pulled threads.
I picked up some M8 x 1.00 fine thread bolts, carefully drilled the holes to match the banjo bolts, annealed and resurfaced the copper washers and everything went together perfect. The lines are snug and no more leaks. While I know you can get longer bolts from the usual sources, I needed something done NOW.
Here are some pics of the oem banjo bolt showing how the body (yellow paint) protrudes. Fresh copper rings may be all that is needed initially, but with time they harden and compress when servicing and then there's leaks. Seems to be right at the edge. Definitely worth considering if you are having issues like this.