Often times, the difference is something as trivial as engine mount styles (lenghts/angles) - which in the case of an SL vs. an SEL/C would be different due to the different dimensions of the engine compartments.
I'm not saying that is the only difference - I'm guessing that is one of a handfull of small ones.

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D