buy a hand held vacuum pump at Autozone or whatever. I would get a nice metal one if you can find it, you need one for this car, thern start pulling a vacuum on your lines until you find the one that leaks, fix or plug it. since you have the door apart pull a vacuum on the two sides of the actuator. if the actuator is bad, replace it or plug the line, if it is not then you have a cracked hard line. you will need to trace it back under the plastic tracks on the floor

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)