As for wd 40 I don't care for it much it will dry off few days on metal, on belts I don't use good for checking for vacuume leaks spray on suspected leak area while running aside from that ,I swear by washing belts in ( gas on rag) gasoline yes gasoline I know not good for rubber but on car belts that have started squeeking it is better then anything I know .that said a chronic sqealer "proubly will need replaced, and the drive pully sandblasted .Aside from that as a test on the road for voltage drop ...try turning on everything and heater fan to(on) high it is advisable to familiarize yourself to the speed of the defrost blower on high( when working condition) the lights on, wipers going ,ect that fan speed will be the same at high speed unless something is a rye....slower speed you might not get your car to restart if you cut if off , get somewhere befor your motor dies so much for idiot lights....