This operation must be done with the engine running, for we're looking for a variation in the engine's speed when the brake cleaner is sprayed upon components that should be sealed but perhaps are not, and which also contain a partial vacuum during part of the 2-stroke cycle. These would include the engine seals and the juncture between carburetor and crankcase.
Get your motor running and spray the cleaner as close to the crankshaft bearings as you can. On my bike the crankshaft bearings and the seals just outboard of them are located beneath the clutch and beneath the magneto.
Now, I have not done this myself on this bike, so proceed with caution and skepticism, but: a spray of brake cleaner, which should be the stuff with the flammability warning on it, should not affect the engine's speed when sprayed near the crank bearing seals. If it does, then some of the brake cleaner is being pulled into the engine past the seals, which indicates that the seals are leaking.
Note that if you have non-electronic ignition the magneto will contain a set of merrily-sparking pair of ignition points, which could conceivably ignite the brake cleaner, though that's unlikely. Just be careful. Or, if the other seal proves questionable, simply replace both seals without trying to test the seal beneath the magneto.