Since bringing my Touring over from the UK in 2000, I have been collecting parts for the inevitable refurbishment. In 2006 I bought a pair of URO door seals (BMW ones were NLA then).
Spring forward to now, and I attempted to fit said UROs and found the same problem as most people. My original seals were good except for the part that ran down the B-pillar. So, not wanting to pay BMW close to $600 for their new ones, I removed the B-pillar part from my original seals and used that part from the UROs. Worked a treat, especially as the pair of UROs had only cost $212 inc shipping back in '06.
For those of you that have removed URO seals in favour of BMW ones, you may find a decent market to sell the B-pillar part from the UROs. Every cloud has a silver lining.