The Mercedes PDC 121R is indeed Tankfreights, when I started work at Harold Woods in 1978 we he about 10/12 of them, ‘DC’ was a Teesside registration, so this was probably based there at sometime, they (Mercs) were all on the black oil contract with Phillips Petroleum and did not take kindly to 24/7 running, some were scrapped after 2 years. I drove one for a shift and the brakes put the fear of god up me! This one in the photo must have escaped to an easy life at another depot because I don’t remember any being painted into the then new Tankfreight colours. They were replaced by SedAk 400’s.