What are the SPECIFIC areas to weather?

Many WWII aircraft, especially single engined, operated from rough forward airfields. So mud, dirt, and/or dust on the landing gear and adjacent areas is a good touch. It’s very theater and time specific as what to do.

Also aircraft operating in the desert or from crushed coral airstrips often had the propeller blades scoured to one degree or another by the sand kicked up. 

Don't use other models for reference.

Find photographs.

Don't use restorations for reference.

Look at real life stuff like construction equipment.

Above all, make an effort to answer your own questions. Eliminates bad data.

Also take into account things like service life. Many WWII aircraft had comparatively speaking short life spans. And operational tempo dictated how much they actually flew. 

While certain types such as transports and patrol aircraft may have had longer lifespans, fighters and bombers typically had shorter ones.

GMorrison

Don't use other models for reference.

Find photographs.

exactly build yourself up a library of reference material from either photos you find online or in books.

You have everything right except rust on control surface rusting on navy planes.  They are pretty much protected, plus control surfaces are either aluminum or fabric covered.  As far as hydraulic fluid (red or pink), landing gear areas and bottom surfaces near doors, maybe some hatches or removable panels.  Sometimes, trailing edges of flaps.

Also, visit local airports.  Hydraulic fluid, exhaust stains, in fact most weathering except gun barrels, will be the same on civil birds as military, except maybe to a lessor degree.

My . Everything above sounds good on the right plane at the right time. The only thing I can add is the weathering on the shell ejection ports on the underside of the wing. A small amount of gunpowder residue in the direction of the airflow is OK for a plane seeing moderate to heavy action.

Hope that this helps you a little.

Jim