Hi
Ultra black is good for the job, but i would choose ultra gray as its for rigid pieces under high torque, black is also very good and will work if you dont find gray.
The only difference from the genuine toyota fipg 103 is that the ultra products take about 10 hours to fully cure. While the toyota product takes under one hour to cure. Meaning car can be filled and started quickly.
Toyota showroom parts counter have the product though, they are just too daft to look it up, its called packing in the database. You can also look for threebond 1207B which is the same product as you find in toyota tubes. Threebond products were sold on marriot road Karachi.