Nope. A leak ANYWHERE in the system lowers the available vacuum in the whole system. Let's picture this as a brake system. If you have a leak at, say, the right front wheel then there's reduced and soon NO pressure in the entire system. Remember that vacuum is technically "negative pressure" and anything true of positive pressure is true of negative pressure as well.

One of the problems with vacuum operated accessories is that they do tend to fatigue and fail hoses, connections, etc. over time so that which worked fine when new ceases to work with age. Ford used to use vacuum door locks and other power assists in the 60s but found that they were problematic in just the way that you're experiencing.

So I'd go hunting for those leaks. The lead on the leak under the left foot rest would be a great place to start.

Dan