Have not messed with gasket material yet but will need too shortly. What is the composition of the material? ceramic fiber, glass Fiber ect.? Something to try, referencing back to a customer a number of years ago cutting a type of high heat insulation board on a table saw, about an 1" thick. At normal circular saw speed it was like taking a hammer and beating your way through a poured concrete wall. at apx 1/3 maximum rpm, the blade cut like a hot knife in a block of lard, carbide tipped saw. so possible a thin abrasive cutoff blade ( i do not think the reinforced one the other- it is a dark brown and fairly smooth ) in a Dremel ( not the battery driven ones ) tool or similar might be the trick. You would have to play around a bit for rpm. secondly a containment option of the rope at the cutting point might also be of some help. Another idea using Dremel would be a friction type cut. one of the little ( about 1" dia) saw blades on same arbor as cut off wheel, the teeth would need to be removed and then the resulting edge sharpened to a knife edge maybe single sided or tapered on both sides. Just some random thoughts. All kinds of strange tools come in my shop for grinding an sometimes it becomes quite challenging to come up with something for a particular application.