Remove OLD wing tank, silicone and a tight fit. PITA

[gregsgt]

Super-braid fishing line. I've removed car windshields with that stuff. Very thin, very strong, and has an abrasive texture.

The other thing you can try is a hot wire cutter. You can make your own like in this video.

https://www.youtube.com/watch?v=qqhHAFgIyCc

[Av8r3400]

Abrasiveness to the cutting wire is not to your advantage. It will only damage the spar. A smooth cutting line is better. What ever line you use will try to straighten with pressure and be forced against the spar. Abrasiveness does not help when cutting a soft material like silicone.

(I own and operate a windshield business and cut out thousands of them per year.)