Brake Booster R&R

[Inukshuk]

Three differences I noted are: 1) There is a line stamped in the front of the booster housing which is not present on the OEM unit. I cannot opine as to what the line is for. ...

View attachment 2543360
Seiken on the Left and OEM on the Right.
Line stamped in Seiken unit not present on OEM unit.

Line is present on a brand new OE unit I got yesterday. It is oriented downward on install. Brand new OE Master cylinder has a smaller line in same place.
My opinion is that they are drains. Leaky MC will evidence itself there. If water was to get between MC and BB it could drain there.

Thanks for this thread! Easy job when engine is out.