The reason for flushing the system with fresh fluid is that the brake fluid is hygroscopic, meaning it soaks up water. The water in the brake fluid corrodes everything and makes a mess. The mess has particles that then ruin the rubber.
If it was bad enough to leak, it needs flushing NOW. It takes less than an hour and a few dollars worth of fluid to do it properly. If something was awry causing air in the system, you can expect further problems, if you flush now, you may prolong it and prevent even further problems. Just do it.