What kind of failure to feeds is he having? The round can hang up on the barrel hood, nosedive into the magazine or jam against the ramp.
When you say the guiderod is slipping off the perch, what do you mean, exactly? The guiderod will not stay exactly in the assembly notch after the slide is racked the first time. After the first slide rack the guiderod slips down slightly out of full engagement with the assembly notch but should still be in contact with the barrel after/during disassembly.
The way the gun is made, it's not (shouldn't be) possible for the guiderod to move down so far that it's not in contact with the barrel after disassembly. The only way that could happen is if the end of the guiderod is badly worn to the point that its circumference is much too small, if it's a guiderod with an end that's too small, or if the channel beneath the guiderod has been damaged so badly that there's extra clearance below the guiderod that allows it to move downward too far.
But there's another problem. With the gun assembled, the guiderod end is NEVER in contact with the barrel if everything is the proper dimensions. Instead, the bottom half of the end of the guiderod bears against the matching plastic shelf directly above the slide lock spring and directly in front of the slide lock. So even if end of the guiderod is somehow slipping down too far, it shouldn't be hanging anything up because the end of the guiderod not bearing against the barrel anyway. In fact, other than some incidental contact between the spring and the bottom of the barrel, the guiderod/spring assembly doesn't bear against the barrel at all except during disassembly/assembly.
Finally, the NY trigger spring can make it necessary to hold the trigger during disassembly. In other words, the difficulty during disassembly could be a normal consequence of having an NY trigger spring installed. To strip a Glock with an NY spring, follow the normal procedure, but while moving the slide forward off the frame, depress the trigger.