Clean the tape. As much as I disliked that plastic tape at the time, ( the tape that came stock on my 74 PX10 ended up wrapping the handle of our lawn mover and proved Impervious to gas , oil, sweat, etc) if yours is holding up, keep it. It speaks to the origins of the bike and its time. Even if you replace it with modern plastic, it won’t be the same. You might duplicate the texture but you can’t duplicate the wrapping technique, probably done by some long gone Frenchman with a Galoise hanging from his lips. It’s the one piece of the bike that you can touch and know that some other human ran it though his hands to make sure the job was done.