The "sealing washers" are special rubber-coated metal washers that guard against vacuum leaks.
These were originally installed on your engine, but I don't think your average auto parts store will have them. You will have to get them from a Mustang supplier. Mustang suppliers do sell them...as separate washers, or you can get complete sets of new bolts with washers included.
Regarding your original washers: After a while the rubber wears off and they look just like regular washers, and they may or may not work. That's how my original washers looked. When I replaced my intake manifold gasket a month ago, I went ahead and got all-new bolts with sealing washers. It's sealed up TIGHT now, with no leaks!
*andy* ([email protected])
also known as...***Boss Hoss***
*1965 Mustang 289 coupe*
*1996 Mustang GT coupe*