My one was dealer supplied - cheap and leaking. It was mounted to the front of the left cylinder guard and died being smashed into someones rear bumper while filtering.
Got a new one ... and so far the best place I found is to mount it on one of screws holding the front fender (Rockster, not R1150R).
I was thinking the exhaust mounting screw, but it is a difficult reach - especially with a hugger.
Suggestions are greatly appreciated!!!