Should not need PTFE tape on the regulator, it's not a seal at that point. if you turn it anti-clockwise until it's removed you will find a large spring witha a cap on it. Put those to one side. Look inside there should be a small plunger with a nipple on top, use a pair of pliers gently ease it out. on the end of the plunger is a small rubber seal, if it's leaking it will be there. Plunger may also be worn. A new regulator is not that much but a seal/plunger should do the job