Hi, Koan58 is correct. On Unit 650, primary vents through clutch push rod area into trans, then out vent hole in upper front of trans outer cover. Sort of in front of the upper front nut that holds U plate on for plungers. I seems to work quite well venting primary. Starting 1970 the trans vent was eliminated & now the trans vented into the primary which vented into tube over rear fender. I don't see it making any difference regarding leaking from primary or trans, one way or the other.
In every case the wire jacket & all the parts must be cleaned quite well. Tri Bond works very good & lasts well. Suzuki Bond works very well also. Tri Bond I get is grey which shows on later bikes. That's why I started using Suzuki Bond, it's black which I feel is easier to blend in on later bikes where wire is visible.
Regarding broken wire sheath, that's problematic. To start with the wire must be warmed to make it flexible enough to pull out on early bikes. Easier said than done, but doable. I still often warm wires on later bikes with wire going over top of chain. In both cases I always pull stator & wires at same time so as to put least strain/flexing of wire as possible.
Wire sheath can be epoxied at stator side, but not so easy. I'd fill the entire broken area where wires are. Cleaning....??? Just best you can with compressed air & solvent. Truth be told I use gasoline, then dry with rags & compressed air, then carb cleaner spray, rags & compressed air. When break is down farther I'll clean the same way & fill gap with silicon or Tri Bond. I'm not above filling the end of sheath where wires exit either.
Get worse.... The last 2 stators I dealt were Wassell & Sparks. Both had wire sheath that was too big for 2 wires, so they wrinkled where inner & outer boots go. Silicone is what I used on both ends as needed.
I've seen so many inner boots split length wise & slide of metal tube. I've lately been using the tiny zip ties around boot on tube end, but just snugged slightly, not pulled tight. Will this help? I don't know yet. At least on early bikes you can just gob silicon on outside without regards for looks. Late bikes I want it to look like it's not really been glued.
You have tough job on the early bike. Might be best to force silicon into tube from primary side. In every case cleaning the silicon for next repair is a pain. The wires can leak a surprising amount of oil out though.
Let use know what happens. Thanks.