If adding an oiler to the air system was needed...
Wouldn't we already have one? he asks rhetorically...
Shutters and that's it.
If there is an offending accessory device, and you've decided that a shot of lube is the solution, understanding how oil and rubber may not like one another... do as eagle19952 suggests, loosen the air line to that device, give it a drink, close up the connection, and blow away.
Please, do NOT oil the internals of any brake related devices, for sure, no exceptions. Having the rubber seal in one of those swell and stick at the wrong time, in the wrong position... dragging brakes burn down buses...
happy coaching!
buswarrior