What I did was slice the existing tape with a razor, and then soak the two glass pieces (per filter) in water. The old gels literally melt in water. Razor off any stuck stuff, wash with soap and dry. I put Rosco diffusion -- Rolux -- in each pane, so one diffusion gel and one layer of the #19 Fire.
Tonight I flashed some paper to around a Zone VI level, and did another coin test with both MGWT and MGFB. With the unit wide open and the paper at 3 feet, I did start to see fogging at ten minutes on both papers. Even with both panes closed, there is plenty of light in the room, much more than the 15 watt units I was using before. It's nice to be able to see the clock!
Incidentally, I wonder if some of the reports of fogging from these comes from the fact that the filters are some sort of gelatin. Why else would they melt in water? Could the company have used inferior filters? The Rosco gels are polycarbonate, and I've had some of these for 10 years that have never faded or cracked, unlike what I found in the Duplex: both the gel and the diffusion were paper thin, dry and brittle.