Installation of PGC Slide on KSC G18C

CHING, I'm having problems installing a PGC metal slide onto my KSC G18C. Here's the problem.

When the blowback unit (Part 250) is taken out, the selector is fine and can be rotated around. But after I put it back into the slide, the selector is very tight and can't be turned, even without the 3mm ball bearing. Also, when I assemble the upper and lower together, the slide gets stuck and it appears that the rod on the selector gets into the way (it's slightly bent I think). Is there any CHING who worked with PGC slide can offer me some help?

Thanks alot.