Well it helps to have some reference for us to comment on.
I assume you're doing the winter camo one?
-Russia-1943-0A.jpg)
The white is actually a whitewash, hastily applied over top of the underlying camo. The white would scuff off around the most used areas, around hatches, or wing walk areas (on fighters).
My only main concern is that this airframe was a much-later He 111H-16 model, and while it looked similar to ours it was definitely a later frame in power and payload capabilities.
There are plenty of winter camo He111s, though, and to answer your question, you can wear it in specific areas, you can add some grain and application variation to it, and if you want to simulate that some of the whitewash is coming off, due to moisture/snow/rain/airflow, you could show it fading in key areas...
-Russia-1943-01.jpg)
Take a look here... Note the area behind the canopy where people might need to lean in to work on something, or where windows might open.... Note the tail as compared to the back of the fuselage. Note the hard masking tape used on the glass canopy on the nose (it wasn't worth masking off every frame most times).
Note that the paint was not smooth -- it was rough, like a matt paint. The exhaust and oil stains in the above picture are somewhat common because every nook and cranny in the rough surface of the paint would gather soot or oil and retain that stain for a long time. To clean it off would remove the whitewash, too, so you get bad engine stains on some of these winter camos.
Note also the wear by the top of the back stabilizers. Some of that could be exhaust, as the stains trailed backwards. Some of it could be underlying green showing through, as this was an area that could be worked on, or covered up, and might have more wear.