I've seen the same - the only thing I can figger is that when the filter is nice and clean and has very little resistance it doesn't hold any fuel in the cup - some elements have more resitance even when new (based on microns of filtration). I would then think the ones that show nothing in the glass are not as efficient as the ones that do. Just a wag.been there done that.talked to a guy that has a 57 and the same glass filter and he says his allways runs with with no gas in the glass bowl.well it looks like it doesnt have any gas in there.he said he nevers has any problem.i just cant understand y each car i see that has a glass bowl it differs from car to car bb or sb it doesnt matter.