I do not know about Permaguard, I use Liquid Glass and it seems to do an excelent job. The calcium here in the water is so bad it tool CLR to remove it from the fiver. Nothing else would touch it short of rubbing compound (parked near a sprinler system). Afer removing the calcium I applied liquid glass to the exterior and let the sprinklers pound on it for 2 weeks. When it looked good and nasty out came the Meguiars Quik Detailer which quickly removed the stains with out resorting to the CLR again. I Also use Liquid Glass on a 1970 Plymouth Roadrunner which use to tour the shows. This car was painted in 1986 and the only product used on it since was liquid glass and it still looks like the day I painted it. I understand there are other products available now but I am not sure I am ready for a change until there is indisputable proof of something better.