You can get plastic razor blades anyplace that sells painting supplies.
They're my usual go-to solution for things like these. If the old sealant has gotten too hard, you may need to upgrade to an actual steel razor blade in certain spots.
If wielded correctly and changed often (keep at a very shallow angle, don't let them get notched), razor blades won't scratch the aluminum. Just inhale deeply and be patient...
2002 Suzuki DL1000 V-Strom, Dark Metallic Space Blue
1983 Suzuki GS850G, Cosmic Blue
2005 KLR685, Aztec Red - Turd II.2, the ReReTurdening