I was going to flush my brakes on my 20 year old car today because the reservoir had gotten a bit low since I last flushed them 6 years ago. I got one corner complete, but realized it was late in the day, I was tired, and I was losing light. Therefore, I'm going to do all four tomorrow or the next day. Do you think I need to re-purchase fluid? I know it's always emphasized new fluid is important, but would 24-48 hours after opening, with the cap tightly on, be a problem? Only about 1/4 of the fluid is missing from the container. Thanks!