Yes Michael, there is a felt washer that sandwiches in between the mag and case. Getting the thickness right is tricky, or buy one. they will weep a little oil from there, but after the felt is saturated and all claggy, it will not be particularly noticeable. Engine breathing problems will increase oil leakage here and elsewhere. 

 Let us know how you go, pics and small article about bike  would be great for the club mag.