I get the blower off my 1967 GM 4107 bus on the bench for tear down and inspection The blower is seized for some reason and I’m digging in to find out why
It looks like dye penatrant from the kit to check for cracks. You spray the red penatrant on and in theory the dye will penatrate a crack. Then you clean the dye off and spray a developer on th show the crack by pulling out the dye in the crack. Best guess.