If you've sprayed Q20 and you were good with your aim and it didnt change anything then It's safe to assume the magneto side seal is OK.
If the seal on the clutch side is passing then the bike would be smoky and have the erratic idling possibly, this is because it would be burning gearbox oil as well as 2T oil, theres a rough n ready check of that seal also
Pour some clear liquid into a jar or a testube would be better still, something like paraffin or white spirit etc
put the gearbox breather pipe into this container, start the engine and play around with the throttle and note if any bubbles come from the pipe or if the liquid level drops any (thats why a tube would be best because it doesnt hold much volume)