hey that exact same thing happened to me. i heard the exact same "Sssssss" sound on my ride and also thought it was a tire, but nothing wrong with the tires. i eventually decided the sound had been a leaf caught between the wheel and where the chainstays join the seatpost (i have thought i was loosing air out of a tire before, only to discover it was this). before finishing my ride my fork took a large hit when i didn't clear a ditch and the front wheel landed just below the lip. when i got back to my car i noticed the seal popped up. at first i thought it was the hard landing. but now hearing you talk about hearing a sound like air leaking i'm wondering if that isn't when the seal popped up (however, i never heard a 'pop' sound then, so maybe it really was just a leaf then). at any rate, my fork is also a manny, with the same evil genius wiper seals. to reseat mine, i took off the lowers to try and push it back down. no amount of pushing will move that thing though. I eventually had to, against my own will, take the broadest punch i could fit down onto the edge of the seal without touching the wiper portion of the seal, and tap the seal back into place with a rubber mallet using as little force as necessary. i tried cutting a peice of PVC pipe to fit on it but none of them fit well, and they kept dislodging that metal thingy around the wiper whenever i tapped on them. I'd take off the lowers so you minimize risk to damage anything else, use a punch and with as little force as necessary tap the seal back into place. have the bottom of your lowers on somthing softer then mag but firm, like a wooden workbench, and if possible have someone hold the lowers as you tap the seal back in. and seriously dude, you should be servicing your fork at least every six months. and those who ride a lot and in bad conditions should at least be replacing the oil every six weeks. order a liter of Motorex Power Synt 4T 5w40, it is the same stuff marketed as their "Semi-Bath Oil" except you get a liter for the same price that you would have paid for 4.5 oz.