Sorry to say, this whole thing is fully of "huh?"
First, what exactly is in this "kit"? Who is the manufacturer? Seriously, he sent back "the kit" and they didn't find anything wrong and sent him a whole new one? That would be shocking coming from DSA.
We still haven't established which "guide rod" broke. Or, where it broke.
It is uncommon to break a recoil spring rod. And, even if one did break, making a "custom" one wouldn't fix jack. Did the rod break, or did it separate from the cover?
It IS common to break a gas piston rod, particularly a cheap, non-FN specimen. Making a "custom" gas piston may help if it were done right and with the correct metal; however, it wouldn't make sense to have one made because a FN example can be had for, what, $30?
Does the piston slide freely?
Is there binding on the bolt carrier?
How many springs are in the recoil spring assembly?
If it were the recoil guide rod that broke, did he try a buffer?
What is the barrel length?
What is the gas vent size?
What was the gas setting?
I'm sure he didn't try everything, he tried everything he knew, which isn't much if he's calling the failed part a "guide rod".
FALs aren't rocket science, but you have to get some details before the problem can be understood and rectified.