I have a question maybe someone can answer. The issue that in hot weather with stop-and-go traffic, my 1972 BMW 3.0CS gets harder to brake. It feels like the brake booster has stopped working. The brakes work fine, they just take a lot more leg-power.

I've checked the vacuum line to the booster, and the one-way valve, and they seem intact and clear. Unfortunately, the brake booster is no longer available for this car as a new part.

Does anyone have any suggestions on this??