if a new belt still squeaks then you have a pulley issue. the belt conditioner might have been causing it to slide on a pulley easier for a moment. also, last belt conditioner i checked said its for prolonging the life of a new belt rather than fixing old ones. and even then i wouldnt use it.
2002 GT 5sp. 16x,xxx miles
Steeda Exhaust, C&L plenum, BBK Throttle Body, Steeda Underdrive, Steeda short throw, unknown stage clutch. Rear main leak. Compressor seal leak. Steeda lower control arms. good tires.