It's difficult to say what to do without knowing exactly what your setup is and how you want the effect to work.
If the lawnmower and the oil occupy the same physical space, then you could do something like:
[ > Lawnmower Oil | Oil ] -> [ Oil | > Lawnmower Oil ]
[ > Lawnmower Oil | ] -> [ Oil | Lawnmower ]
which will apply itself as many times as possible, and thus cause the lawnmower to slide all the way to past the end of the last oil.
An alternative thought is to use the again keyword. This has the nice side-effect of looking visually appealing, but you would need some way of storing the direction the lawnmower was travelling so it's not lost on the turn change. For example, using a transparent object called LastSpace:
[ LastSpace | Lawnmower ] -> [ LastSpace | > Lawnmower ]
[ LastSpace ] -> [] ( Just in case something weird happens )
[ > Lawnmower | Oil ] -> [ LastSpace > Lawnmower | Oil ] again
These may not be the best approaches, but they're the first things to come to mind. I haven't tested either of them.