I have been wanting to test my injectors and finally got around to it last night. The gizmo I rigged up was an air pressure regulator connected to a brass gate valve. On the exit side of the gate valve I plummed the can connector from an old R134A installation hose. The R134a can and the M103 injectors are the exact same thread size. The only readily available solvent I had was ether(starting fluid).
I filled the injector with ether and connected the R134A connector.
With the regulator valve I was able to increase the pressure until the injector "fired" which in most cases was about 45 psi.
Well, every one of the injectors has a one sided spray pattern. Some 'sang' and some didn't. Two of them leaked below 40 psi.
While my test was most certainly 'shade tree engineering', I feel that it identified a definite problem area. I'll order all new injectors. It certainly can't hurt anything except my wallet.