I agree. It's very probable that those 'stains' were not there before the crash-landing.
The photo above is interesting, as it shows what is very possibly the original 'saddle' cowling over the guns, which has a different colour demarcation and pattern to the one shown in the 'crash' photos, matching the main cowling, and agrees with the statements from 50+ years ago, regarding a replacement saddle cowling.
At that time (mid 1960's) it was suggested that the top of the saddle cowling might have had a mottled finish. This may be so, but it could also be the effect of dust and dirt from the landing. The aircraft came down in a harvested hop field, ploughing through the light, dusty soil and hop roots, throwing up a lot of dirt and dust, as evidenced by the tones on the main wings, and the top of the main cowling, and also the dust accumulated around the spinner and in the engine bay.
At the very least, this section of the cowling certainly has a higher demarcation, and, if not mottled, then it is a lighter shade of possibly RLM 02.