Has anyone here from SA asked for or done their own tests on the fuel they provide?

Mostly I am curious about water content, but also glycerin and cetane. I ask because the latest batch I bought runs a bit rougher and I am seeing a bit more smoke. It isn't a problem (I hope) but it made me wonder......

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT