hi dave,
Oh the joys of old jap bikes!! etc
Do you have a mig welder or know someone who has??
See cmsnl for the exploded views which will help.
Broken bleed nipple, sorry don't know size and thread but, a method I use very successfully to remove broken nipples, buggered screws etc is the mig method
I assume the caliper piston is free, and goes back in with hard thumb pressure, if not then don't disconnect the haudraulics yet as you need it to free the piston easily........
Place caliper in hot water and pump away the brake lever till the piston comes out as much as you dare, BUT NOT all the way out yet.
A "g" clamp ( protect the alloy with wood etc ) can be used as a "spring" to exercise the piston till it frees off, some brake fluid can be used as a lub when the caliper is out of the water. Excersise the piston till it frees off, then strip the caliper etc......
With the caliper off the bike, mig weld a blob onto the cleaned broken nipple ( yes I know its flush with the caliper body ) , Clarke 100 mig welder, full power with speed set to 5 1/2 to 6 ish, 0.6 mm wire, 3 to 4 second "burn".......
Allow to cool, then weld a blob to the "blob", allow to cool, repeat till a good blob is there, then weld a "tapered" end bolt to the blob and allow to cool for 20 secs, then try gently to undo the "bolt"........
If it shears off then repeat exercise.........
Pic will show "buggered screw" welded to the bolt.
The thermal shock helps to free off the broken nipple and unscrew it out. DRILL OUT AS A LAST RESORT! and at your peril.
"But doesn't this bugger the caliper, melted alloy etc. ?" only if you are not carefull.
The same could be tried with the pad pins which are a push fit into the caliper, both sides.
Problem pad pins can be tackled but removing the caliper from the bike, saw each pin centrally and split the caliper.
The hydraulic side can be stripped and then some heat appled to expand the alloy a bit and free off the pins ( some heat, with pin clamped in vice, a gentle "rotation" a few degrees both ways then some lub ( water is good , free and bio friendly ) and hey presto.........
Similar method with the "sliding side".........