Seals broken on sealed goods

I bought 2x 5L Caltex Delo super gold diesel oils from Midas. There are obviously many different types and grades of oil on the market and at many different prices obviously.I specifically want Caltex Delo for diesel engines. I paid R358 for the oil and when time came to open the containers I found that the seals under the cap have been broken, this is not the first time, on a previous occasion it was the same story also at Midas Alberton.... In my view that seal is there for a reason, just like with any other container one buys that is sealed...why are the seals that Caltex put inplace broken and how do I know I'm getting Caltex Delo and not some cheaper oil or additive?....