Power brake problem with '83 300d

I recently replaced the master cylinder and the two rear brake calipers on my '83 300d.
When I installed the master cylinder I goofed and put washers between
the brake booster housing and the nuts that secure the 2 cylinder bolts to the booster. Of course this caused a huge vacuum leak and it took me a while to trace the problem to that improper washer installation. So I fixed the problem and the vacuum returned to normal.
It's been about two months since the installation of the new cylinder, and I'm losing a lot of brake fluid. The secondary brake fluid chamber (the smaller one on the reservoir) seems to lose fluid over the course of a couple of weeks after it's topped off. I'm not sure where it's going. No apparent leaks at the rear calipers (I am assuming the rear calipers are fed by the smaller brake fluid chamber.) No apparent leaks from the front. That primary fluid chamber doesn't seem to lose any fluid at all.
I've topped the fluid off twice now since the repair. I noticed yesterday that the brakes don't seem as firm as they used to. Stopping distance isn't as great as it used to be. If I drive the car for a few minutes, the problem goes away somewhat.
I'm worried that the brake booster might be going bad, especially in light of the fluid loss. Could it be the master cylinder is already leaking, even though it is new?
When I was installing the cylinder, I bled it by having an assistant hit the pedal while I opened and closed the fittings. Might I have damaged the seals this way? The pedal travelled pretty far down while we were doing this.
Perhaps the damage to the brake booster was done by the old cylinder? It went bad in a spectacular way (you know, loss of pressure at stoplights, on inclines, etc.) and the fluid was in terrible condition for many years.
In any case, I have had absolutely no abnormal pedal travel with the new cylinder. Only have had problems with the power brakes.
Any idea what's happening here, in light of the loss of fluid from the rear chamber of the reservoir?
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Yep, you got a leak somewhere... Smaller reservoir is to the rear brake.
Did you bleed the master cylinder before you install it?
Double check your rear calipers to see if it is leaking... have someone step on the brake while you look back there.
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