My first thought is to modify a Plarail Hiro into a DB Class 41. Hiro already has red running gear, which avoids the constant paint wear, and his boiler cladding is less busy than the standard D51.
As far as a parts source, ESCI did a 1/87 static model of the Class 41 (and Class 50) that are still pretty easy to find on eBay. IIRC, Italeri has either already re-released them or plans to at some point soon. That *might* be cheaper than trying source parts from a Marklin or other ready-to-run HO model.
I notice a lot of similarities between post War and modern Japanese and German diesels and electrics. Right off the top of my head, I can’t think of an exact analog but there’s likely to be a close match somewhere.
EDIT: Darn, I forget that Diesel 10 is based on the BR Class 42 “Warship” which is, in turn, based on the DB V200!
I think it could be done but the model had to be changed abit at the front above the Face. With alot of patience its possible to make it look pretty awesome but i think thats too much for me as a fresh starter. I thought of something smaller like a Light mod or maybe Tracksounds that react to the rotation of the wheel.
For the steam loco, the fact the switch is exposed as well as the axle makes me think you're missing a panel that goes over that whole area. If this is the case and someone who has one can photograph and measure the piece I could probably print you a replacement.
As for the first one, Mr Ripley is the king of battery corrosion issues :-)
Happily collecting things all my life...
These are pretty common as far as the one with corrosion, I would say just look for spare and swap it out. You could try cleaning with distilled vinegar but it maybe too far gone.
Could you just glue a small strip of plasticard over the middle of the axle to hold it in place? If not I could easily print you a piece to glue in that would fix the issue.
Happily collecting things all my life...