On my Previa van, the seat covers are very dirty after 27 years of use in Thailand, a very dusty country. I have removed all of the seats, but instead of trying to shampoo them, while they cover the foam rubber, I would like to remove them and have them cleaned. Other than being dirty, they look like new. Have any of you tried removing the cover from the seat? In addition, it appears that the front seat headrests should be removable or possibly adjustable, but I can't find a button or latch to push to release them like the ones on the rear seats. Is there a secret latch somewhere?