Thanks!
The master has a scratch inside. So its yunk. I opened the master and filled it up. But the system is only good for a few month than too much air is inside.

The S-10 looks similar, right? But it is not sealed because I have a 89 S-10 and I can bleed on the slave the common way. Is the 91 the next generation from mine? Mybe I should measure my Chevy set and try to use Chevy tech in the car :-D