Joel, I've successfully repaired several Higel transmission frames
and other intricate pot metal fittings in the past without resorting
to welding or further damage.

When the break is clean (and it usually is as they tend to snap in our
own hands, drat the luck!) I fit the pieces together and ponder where's
the best place to drill two or more 1/16" holes through so that the
pieces can be 'sewn' together with several loops of very thin beading
wire, as many 'turns' as the holes will allow to pass.

Yes, just like sewing on a button.  Visualize the wire 'runs' as braces
against the directional forces acting on the position of the part or
tab that broke off for the logical angle and position of the drilled
holes.  I think I usually use brass, though some other wire may be
stronger; available at any craft or hobby store.  The idea is to draw
the pieces together snug as before they broke.

Being sure the parts are thoroughly cleaned of grease and dirt.  Before
reassembly I wash transmission frames, gears and fittings in water
cleanup-able "Dunk" (Canadian Tire Auto Department).  The final strong
finish is to coat and shape a good epoxy over the repair site.  In some
cases you might even lay a headless pin or two against the straight
flat sides spanning the break and overwrap them and the stitch repair
tight to the frame with the wire.

I use five-minute epoxy as it sets quickly while you shape and smooth
the bond.  After it's cured overnight and nice coat of black paint is
applied, you'll be hard-pressed to spot the repair.  (I've used black
nail polish too, in the past, although automotive satin black trim
paint is a good match for the original).

The key is to keep the parts mated tight and square when stitching them
together.  I repaired one frame that was broken in five pieces this way
and it's as strong as the day it was done 15 years later.

On another note: in cases where the intergranular corrosion has warped
the frame but it's still usable, the roll chuck axle can be easily reamed
true to eliminate binding against the shafts.

Dave Kerr,
in a lovely Currier & Ives winter weekend snowfall in
Stratford, Ontario, Canada