i have had the same problem with my rt125
on it i removed the system from the bike
as plastic does not like brake fluid
the master cylinder will come off with the rear caliper without taking the hose loose
if its like my rt
the pads are ebc fa 197
and it needs a clean out and flush
if you need a new one
try this
for the mastercylinder
http://www.yoyodyneti.com/ProductInfo.a ... 10.4776.83kaw klr650 2008 and newer looks like same rear caliper bn125 kaw chopper may be the front
or some of the royal enfield bikes use the fa 228 pads of the front ??
a good clean got mine working again
dave
bleed by forcing fluid from the rear caliper out into the reservoir this is how i got all the air out
hang it from the reservoir this makes the air flow out better