I think TL here is Teil, part. Me 262 starter engine was a two stroke piston engine, so it is 5% two stroke mixture.Unless I am reading it wrong, the "20 TL Benzin 1 TL Oel" indicates that you are to use 20 parts gasoline (aka Benzin, technically any grade but even motorpool petrol would be OK) to 1 part oil, measured in teaspoons. Does that make sense for the amount of fuel needed for the starter motor? Or is it just the ratio of 20:1 gasoline to oil?
TL = teelöffell = teaspoon = ~5 ml