Hi Andrew,
It's OK I'm used to being called by my last name.
As far as I can judge from the black and white pictures the light gray color RAL7011 was used instead of the black and the red part could be black. But it seems that most where simply painted uniformly gray either RAL7011 or 7021. Especially from 1943 onwards all was painted panzergrau (7021). This is from official painting orders, but the Germans had a habit of field conversion/painting.
About the red/black/white camou pattern, I have no war time photographic evidence of this. And judging from the sources so far no BR-52 during the war where painted red/black. But again the Germans had a habit of field camouflaging things so anything could be possible.
The pattern might just be a mistake taken over by a modeling company from a museum locomotive, I have seen pictures of a BR-52 painted like this in a museum, but museums are notorious for having wrong colors on equipment.
Don't forget that the brake lines are black rubber and that the buffers had a white rim around the contact surface of 50mm (scale 1:1) wide. This was because of black-out orders, no lights during night time.
Oh by the way what you call sand injectors are the brake lines. If another car/locomotive is put in front or behind this locomotive these lines are connected so compressed air can pass through in order to have the trains brake system function. You will also find them in the same location on your K-5. So if you put the K-5 behind the BR-52 or in front (which could look realy cool) you should find a way of connecting these.
http://farm1.static.flickr.com/163/435868811_22f2dac453.jpg?v=0Sand is only fed to the drive wheels not the front boggie, it has not purpose to do this.
And I'm no real expert on specific parts of railway stuff (I'm more into panzers, but I seem to know a lot of train-minded people) but those vessels/canisters you ask about a probably the compressed air tanks. If I'm not mistaking the K-5 also has these on the underside of the carriages.
I agree with you on the eagle, I will probably put it on as well and paint in the swastika. It makes it look better.
I still have to check if the eagle looks the right way, because someone told me that on the 1:35 archer transfers for the BR-52 it looks the wrong way.
Keep the pictures coming.
Regards,
Pascal