I had same problem with the brake part rubbing on the case and I cured it by fitting a small square of canvas/rubber between gearbox rear mounting and frame boss. I believe there was a spacer originally in that position. (Carl will know for sure !!)

Mike.

A stroker is always marginal on the crankcase ventilation so probably the cork washer at the crankshaft drive gear can't keep up and pressure is building up in the primary/transmission. I would recommend discard the disk and use a PCV valve on the vent.tube and change the cork ring regularly. A telltale of rised transm.pressure is oil leaking from the tiny ventilation hole in the shifter cap on the transm.tower. And that hole must be open.

Fresh oil is many times translucent and spot the source of a tiny leak is very hard. Threads are in fact not tight and oil leaks can be found going right through nut and stud threads, and I had to resort to tie strips of clean white paper strips around oil lines, valve spring covers, shifter tower, and various studs and nuts before going on test rides, in order to find leaks. I use locktite on ALL threads, and ALWAYS, except head bolts and cylinder exhaust nuts. And sometimes even that isn't enough but have to use fiber washers under certain nuts in order to avoid leaks. The long stud at the clutch cover lowest point is particular problematic and one of them where I use a fiber washer.

The talk about rised pressure in the primary/transmission promts me to make a serious general warning to all with open band rear brake at left. Do not ride without the toolbox mounted at it's proper place on the frame, because a tiny oil leak at the clutch shaft worm gear can result in drops of oil flying with the wind right in and between the brake bands. The result of that is sudden and total loss of brake function. I have been there, done that. The toolbox position shield from those oil drops hitting the brake. 

Don't use the felt washer behind the knurled nut at the clutch worm, use a tight fitting, fairly thick O-ring instead. Use soft setting locktite to seal the steel distance oil tight on the shaft. And glue the nut. The added friction from the O-ring won't be a problem, you get used very quickly to the added resistant in the foot clutch.

An oil leak from the tell-tale hole under the chain sprocket does indicate that the cluster gear axle is loose in the bushing inside the gearbox and is a indication that it needs to be addressed sooner than later. 

Thank you for taking the time to write that informative response. I think you are right as the 101 stationary has not leaked oil. On stopping after that extended run at around 55mph with this stroked 101 there was oil lost and blown all over the rear. Fortunately it did not reach and contaminate the brake band. The tool box was covered with oil though, and as you say, it has another purpose as a guard. So the crankcase reached too high a pressue and pressurized the primary case and also maybe the gearbox. That seems plausible. I’m still new to a 101 and there remains much for me to observe. I don’t have anything more to say other than I now need to study crankcase venting. Thanks again, for the “starter.”