This is the flexible rubber brake hose for the left hand rear caliper.  This hose runs along the rear trailing arm and is the outer (longer) hose of the two.  The inner hose is CD6243.  These two hoses have been known to swell and block internally and are the most common cause of a brake caliper sticking and overheating. 

Also: This hose is used for the Height Control Valve:  this hose is the low pressure return hose for each rear height control valve.  Cars prior to vin#7405 there are 2 of these hoses for the height control.

From VIN 7405 there is just one of these hoses for the return (as well as the two valve return hoses).

This is also the flexible hose used on the early Silver Shadow front height control valves. They are x3 of these required for that valve (sold each)

1966-1980 Silver Shadow, T-series, Shadow II, T-2, Corniche, Silver Wraith