Don't worry about it
I wouldn't be too concerned. I did West & East Africa on 640 Adv and LC4 400 2002/3 and had no bad fuel issues. Try to fill up at the main brand stations (Shell, BP etc). I'd heard that smaller "uncle Joe's" corner stations often dilute their fuel to be able to sell more so I avaoided these.
I did fit a big(ish) inline fuel filter in between the fuel tap and fuel pump. As a precaution I took a small bottle of Octane booster to use if I heard the engine starting to ping because of low octane fuels ... I only used this once after filling up at a dodgy little station in Nigeria. If I knew that I would be pushing the fuel range I carried an extra 5 ltrs strapped to my pannier rack & topped up into my tank asap.
It's unlikely you'll find any unleaded fuel south of Morocco (at least that was the case 3 yrs ago) which over a long time can clog your catalytic converter. Still got my 640 and it still runs fine after running on leaded fuel for 9 mths.
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