Good morning, Tony;

Brian does have the idea, but if I can offer a slightly modified suggestion, try setting the aperture to something like f:16. Then with the shutter set to "B," depress and hold the shutter release while you look at the lens diaphragm or aperture leaves. If you can see sections on the leaves where there seems to be oil, then the lens will need a CLA.

With the lens set to f:1.7, the aperture leaves should be all the way open, and you probably will not see anything back to the film plane.