So, you want to sell pure gbl and label it as a metal cleaner? Or are you making a product 'with' gbl as the active constituent?
If you want to sell it pure, it doesnt surprise me that the government wont let you sell it
If it were me, I would dilute the gbl with NaOH, but thats just me.
If i were you, i would dilute it with something that actually helps to 'clean metal'!
Pick a solvent, any solvent