Looks like Prem50 "petrolatum" impregnated tape. Darker than denso which is putty coloured, otherwise similar afaik.
Lighter fuel or WD40 should clean it up.
For the first transatlantic cables they used gutta percha, a rubber polymer from trees. When they pulled them up decades later, the joints were still perfectly sealed. They used it for filling root canals in teeth too. Nothing to do with your gas pipe but, just in case you're .....