you MUST have pushed the caliper pistons in to fit new pads , that is o big no no

the abs thingy ( can`t recall it`s name , the big alloy thing ) will pobably be full of crud now or you can damage the x5 master cylinder by pushing fluid back through system , this is true .
in future when pushing pistons , first open bleed valve on caliper to allow old fluid to escape .
ok so you probably need new master cylinder seals because you did not educate yourself on correct proceedure for x5 , you can`t always rely on forum diy guides . hope it works out ok for you . buy a manual from Bentley Publishers Home *-* Bentley Publishers - Repair Manuals and Automotive Books