I'm not sure about the MC16, is the two stroke oil definitely under the seat?
On the MC21 it's a clear tank to the right of the petrol tank.

The other fluid the bike needs is coolant. Same as most cars and bikes. Somewhere on the bike will be an expansion tank, so that as the water gets hot it can expand into the catch tank. When the engine cools down again, that fluid is drawn back into the cooling system.

This may be the other bottle you describe. Is there a pipe from it to the radiator?
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