86 brake booster

[jaekl]

Looking for some opinions (actually cheaper fix). A while back on cold days I'd have a vacuum leak from the master cylinder, cabin side. Typically, it would leak the most with a light foot and stop (leaking) when pressed all the way. Now it leaks a little all the time except when fully depressed.

I've just assumed it was the seal around the push rod, but doesn't that requires replacing the entire booster. Or is a simple repair possible? It's not my daily driver and I have full braking power. It's at the age where I'll nurse it along with the irony being if I end up replacing it, I should have done it a while back to get the most usage.

My understanding of brake boosters is vacuum is maintained on both sides of the diaphram until the brakes are applied. Then the cabin side is vented so that atmospheric pressure helps push the brake rod into the master cylinder. Obviously, I haven't taken it out yet to assess the situation. Just trying to lean on the experience here on the workings of a booster.

Thanks,