BMW cross-lace wheels (tubeless) present quite a challenge when it comes to truing. These wheels are built like no others (except Moto-Guzzi who bought licensing) and are so unique they are patented. There reasons why these wheels are diffcult to true. The first is the lace pattern itself. The nipple is located in the hub vs. the rim, and the spokes cross over the center to the other side of the rim. This unique design prevents the rim from being moved into true with spoke tension like a typical spoked wheel.
If the rim is bent, even slightly, it is impossible to get the wheel true. The wheel must be completely disassembled, spokes and nipples thoroughly cleaned and lubed, rim straightened (or replaced) and then re-assembled. Only then can the truing process begin. This is a very time consuming process, but each and every step is critical to the final outcome.