First, I do not believe that your machine has a mechanism that is called an engine brake (although some diesel engines have them in various forms). Four strokes tend to use the engines compression to help slow the vehicle when you let off of the throttle while the bike is in gear and the clutch is out, this is often referred to as engine braking, but it does not use any "brake" mechanism.
Tons of oil is not necessarily a good thing, and can be as bad as not enough.
Since you say that you have no compression, I am inclined to believe that it's time for you to pull the top end and take a look. At a minimum, you should plan on replacing the rings. Rod is probably right, and your reluctance to believe that this is your problem does not prevent it from being your problem. If replacing the rings doesn't fix your problem, then you have far larger problems to fix, so you should hope that it's just your rings (it could be a shattered piston).