The sleeve (1857 840) was available for installation at the rear of each arm for severe-duty applications -- police, taxi, etc. There's a TSB on it, but I can't find it at the moment. The sleeve could also be used to take up the slop if the bushing wouldn't fit tightly; that may be why the FPC shows "2" instead of "AR" (as required); perhaps it was assumed that by the time bushings would need replacement, sleeves would be warranted.
I can't imagine any harm that might come by installing all four sleeves, if they'll all four fit, on general principle.
