I recently had great success removing the stubs of cut-off lead
tubing from a tracker bar by soaking the bar for several days in
"Purple Power" degreaser (widely available, but only $5/gallon at
"Dollar General'), which turned the "cement" around the tubing/nipple
juncture into a "goosh" with the consistency of oatmeal.  (Much nicer
than soaking the bar in something more odorous, and flammable!)

A happy side-effect is that this stuff cleans the bar without the
need for methods that leave polish or fibers in the holes.  (I've left
a badly-corroded brass flange rail in it for a while, and it came out
truly gleaming!)

I also had great success (outdoors, wearing a P-95 dust mask and
safety goggles) removing extremely corroded lead tracker bar tubing
from a wooden channel board by running decking screws into the top of
each broken-off tube with the corresponding "star-drive" in a manual
screwdriver handle, and then prying upward with a large pair of
needle-nose pliers with a right angle bend on the end.

The "elbow" of the bend, placed on a small wooden block to protect
the channel board, created a fulcrum; and the tips of the pliers,
squeezed under the head of each screw, pulled the tubing out
beautifully!  (Even with all of the shellac picked away from around
each tube, efforts to pull them out directly had almost exclusively
resulted in breakage due to the extreme corrosion, and little clouds
of toxic dust blowing about.)

Next, I blasted as much lead dust as possible out of the channels
with an air compressor (also outdoors) in preparation for sealing
them with shellac.  I'll twist the stubs of lead tubing off of the
screws and wash the screws for re-use, then these stubs and the
larger portions of lead tubing from the system will go to the tire
store to add to the discarded wheel-weight barrel.

Gordon Stelter
Athens, Georgia