My '02 B12 had a bad wobble with the OEM Michelin Macadams, and it got worse as the tires wore (and cupped). Seems like a common ailment.
Finally replaced (at 12K miles) with a matched set of Conti Road Attacks and now, with 1k miles on the new tires, I still get a very slight wobble if I let go of the bars and coast.
I'm guessing it's not the tires, so I'll check/tighten the head bearings first (and confirm tire pressure), add a steering damper if necessary.
Good luck!
Rob
Gettin' wet commuting every day in the SF Bay Area rain!