I want to buy a 5258 but is it possible to retrofit one of the older electric motors , i have a few boxed ones and want to use electric motors .. is that possible
I think that it is more difficult, cause the battery motor changed 2012 (9V instead of 6V), it's a new motor block.
Look at the locomotive: the axles seem to be further apart than in the older engine blocks. So you can't change the motor block without modifications. Perhaps you can change the motor (in the block)?!? But we don't know it exactly, cause no one saw this motor block in reality.
I asked Playmobil, if the two axles are directly powered from the engine (old RC blocks had/have only one directly powered axle), but they can't answer it (March 2012).
With the older electric motors you have more possibilities:
you can digitize the locomotives and you can have steam (also cylinder steam), lights (light change, control panel lighting, chassis lighting), high quality sounds, electric couplers etc.
[LOOK HERE, in this example it's no Playmobil loco, but for Playmobil locos you can also do it the same way]