Owning a car means dealing with fluids that eventually go bad, and ignoring them just leads to a much bigger repair bill later. A complete brake fluid flush and power steering service usually runs about $400, and you can get the best price by scheduling during quiet early spring garage openings when shops are slow.
You want to separate negotiating the service price from how you pay for it. Get the shop to give you a firm total before you talk about your payment method so they do not try to bake financing fees into the repair estimate.
Remember that the 0% intro APR for 15 months on purchases and balance transfers is a hard deadline, not free money. If you still have a balance left when those 15 months are up, interest charges will kick in on the original amount.