Hydraulic Roller Lifter testing...?

Recently I acquired a 71 340 equipped with a hydraulic roller cam and Comp Cams retro fit juice rollers. One pair seems to be giving me some trouble with noise. I recently removed all the lifters and soaked them overnight in fresh mineral spirts/solvent. Using compressed air I blew them clean including the oil orifices. Is there any method to check to see if there is a problem with the plunger? Its seems a bit easy to depress the plunger on some but not others while using a pushrod in a drill press while the lifter sits in a V-block.