Jim,
If your 1/4" poly ice maker line really is run inside a section of 1/2" PEX, perhaps this is more of a blessing in disguise. Assuming your refer is in a slide out, the ice maker line eventually has to penetrate the frame rail and follow the electric lines through a flex guard and eventually, go up through the slide floor to get to the refer.
In this case, the PEX likely ends inside the underbelly on the back of the frame rail. As you'll need to splice the 1/4" poly to eliminate the leak point, consider disconnecting it at the shut-off valve, connecting a new section (tape) to the old section, then pull the new in from the outside of the frame. Make your splice outside, then push the splice inside the frame.
On my new unit, I decided to upgrade my 1/4" poly to stainless steel braided residential ice maker line. I tied a 20 foot section onto the original poly under my kitchen sink and pulled it through the underbelly. I did have to cut a 3-sided flap in one place in the underbelly to reach in and find the line to help it along. That flap will tape up nicely with Scrim Tape.