I'm not sure exactly what you mean by the rubber guide is "split"…. Are you talking about the rubber strip the edge of the the glass goes into?
If it's that one, it goes around the glass edge, then down IN FRONT of the tweeter panel, where I'm pointing.
This is the rubber channel we suggest be kept lubed with something like pure silicone spray, or Teflon silicone. It has several channels within it, (not just the channel the glass edge goes in) and I wonder if that's what your guy means by "split"?
Also, some of us have widened the FRONT vertical metal track that rubber ppiece fits in to. I found that's where my window seemed to slow down a bit when going through the top part of that metal track. So I keep the entire front vertical part of the rubber strip well lubed there
WIDENING the metal track, so the rubber gasket has more room, so the glass edge doesn't get squeezed as tight and add silicone lubricant so the glass slides easily within the rubber channel.
1st pic BELOW has the rubber channel within the metal track, and the window edge is within rubber track.
2nd pic shows I pulled rubber away, and used a screwdriver to widen the metal "C" track. See all the scratches on the side of the vertical metal track, that's from me also using various pliers to bend and widen the track.
You can completely remove the rubber gasket, it's comes out/in very easy.
Hoep this helps!