We've had quite a few folks do the Shasta BDT this year. You may get more traction asking in the FB group. Last status was that Mud Creek remains impassible when circumventing Mt Shasta on its SE flank. I'd still recommend driving to Mud Creek as there are views of Mt Shasta along the way. You'll need to backtrack the way you came and then take 40n88 to highway 89, head east, left on 40n34y (Esperanza Road), right 40n13, left 40n15 which will put you back on the route (forest service road 13).