2006 BMW K1200S
Sounds like an internal leak. Even if you have air in the system you should still be able to pump up some pressure if your master cylinder and slave cylinder seals are holding tight. If your master cylinder is leaking past it may or may not build pressure but will not hold pressure as the fluid escapes back to the reservoir. If your slave cylinder is leaking past you will have fluid coming out and going all over the place when you pull in the lever. So can you do several short pulls on the lever to build pressure up?