oily morning puddle's got me sumped

The fact that this morning's oil puddle was bigger and cleaner than usual just after I topped up the gear oil, may indicate that the leak is from a mid level part of the engine, such as..

1) the gear changer (hope so)
2) under the flywheel (there was a bit of oil under there last time I looked, but didn't look like it was coming from the actual seal.
3) clutch cover. (has threads stripped on one of the bolts. I last did it up with some gasket goo 2000 km's ago.
4) rear hub.

I wonder if it is possible to put talc on the motor (or something) to see where the source is. Once the scooter starts up the oil from leaks blows all over the place causing mass hysteria (well, difficulty tracing leak at least).