if your bit has stopped removing material you have work hardened the bolt.
use a new bit, plenty of oil, SLOW Speed,lots of pressure. only 10seconds or so and stop and clean.
use a small pilot bit at first.
 Any interest in a drilling jig to hold the drill in position so  they can be drillled while in the car?
I am trying to judge interest to see if it is worth manufactureing them.
mike