A stitch in time saves nine.
You use this proverb to say that it is better to spend a little time to deal with problems or act right now than wait. If you wait until late, things will get worse, and it will take much longer to deal with them.
It is often shortened to "A stitch in time."
I advise fixing the leak now. If not, you might need to replace the whole engine later. Fixing the leak costs $50, but you need to pay at least $1,000 to replace the engine. A stitch in time, you know.
If you have an idea for your final research paper, start writing today. Don't wait until the end of the semester. A stitch in time saves nine.