Part No. 42-6915 (oro2u.com)
MASTER CYLINDER RESERVOIR DIAPHRAGMS [Sold Each]
Made in Japan.
Here is the fix for leaking Master Cylinder reservoirs. Available for many popular applications.

Cross reference numbers ONLY. 56A-25854-00-00, 32-7708
1985 MOTOCROSS - YZ125N FRONT MASTER CYLINDER
1985 MOTOCROSS - YZ490N FRONT MASTER CYLINDER
1985 YZ250N FRONT MASTER CYLINDER

1986 MOTOCROSS - YZ80S FRONT MASTER CYLINDER
1986 YZ125S FRONT MASTER CYLINDER
1986 YZ250S FRONT MASTER CYLINDER
1986 YZ490S FRONT MASTER CYLINDER
1987 MOTOCROSS - YZ125T FRONT MASTER CYLINDER