1930 model 20 engine breather parts.

Hi, I bought a 1930 model 20 and have had a few teething problems. One thing I noticed was that the engine breather to the rear of the crankcase appears to have some bits missing. The disc that should sit in the union that's screwed into the crankcase is missing, as is the spring. The plunger that has the recess for the spring and seats against the top cap nut is present and seems to be okay. Would anyone have these two parts (spring and disc) and is willing to sell them to me, or can anyone give me measurements and material type for the disc and details on the spring. 

I know it looks the same set-up on a 1928 model 18 that I was kindly shown at a recent rally.

Any details will be appreciated.

Thanks.

Pat.