A CITATION 500 IS REVERSED IN COURSE AND CLRED TO 'DSND' WHEN THE PLT EXPERIENCES A SLOW LOSS OF CABIN PRESSURE. DURING DSCNT THE CITATION COMES IN CLOSE PROX TO A CLBING C5; ALMOST LOSING SEPARATION 40 MI NE OF UVA; TX.

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I WAS PILOTING A CITATION 500 WITH NO PAX ENRTE TO A DELIVERY IN WISCONSIN. APPROX 40 MI NE OF UVALDE; TX; AT 27000 FT I HAD A PARTIAL RUPTURE IN THE DOOR SEAL OF MY ACFT WHICH CAUSED A SLOW CLB TO BEGIN IN CABIN ALT. I IMMEDIATELY BEGAN BREATHING SUPPLEMENTAL OXYGEN AND INFORMED ATC OF MY PROB. I TOLD THE CTLR I NEEDED TO RETURN TO UVALDE AND BEGIN AN IMMEDIATE DSCNT. THE CTLR TOLD ME TO TURN R DIRECT UVALDE AND BEGIN A DSCNT. I DO NOT REMEMBER BEING ASSIGNED ANY NEW ALT. THE CTLR ALSO INFORMED A MIL C5 WHO WAS CLBING BEHIND ME OF MY PROB AND I THINK ASSIGNED HIM A NEW HDG. IN MY TURN I SPOTTED THE C5 AND BELIEVED NO CONFLICT EXISTED. THE CTLR ASKED IF I COULD MAINTAIN MY PRESENT ALT AT ABOUT 23500 FT AND I TOLD HIM PROBABLY SINCE I STILL HAD A LIVABLE CABIN ALT BUT THAT I REALLY NEEDED TO DSND FURTHER. AT THAT POINT I WAS TOLD FOR WHAT I THINK WAS THE FIRST TIME MY ASSIGNED ALT WAS 25000 FT AND HE OFFERED LOWER IF I WANTED TO DECLARE AN EMER. I FELT THAT NO EMER EXISTED YET AND TOLD HIM I WAS CLR OF THE C5. BEFORE THE HDOF THE CTLR GAVE ME A NUMBER TO CALL THE SUPVR ON DUTY FOR ROCK SPRINGS (ZHU). I CALLED AFTER LNDG. I FEEL THE CONTRIBUTING FACTORS WERE 1) THE URGENCY OF THE PRESSURIZATION PROB; 2) A MISCOM OF ASSIGNED ALT; 3) MY RELUCTANCE TO DECLARE AN EMER; AND 4) ATC'S RELUCTANCE TO DECLARE AN EMER FOR ME.