Hello, hope all is well. Welcome to the world of “Z”.
I think this model was produced in the early years of Mini Club, perhaps issued in 1975 or there about. The model was designed as a track cleaning device which has rapidly spinning wheels on the front, which are stated to knock debris off the track, but many questioned its effectiveness. It was essentially the same until the motor was upgraded to a 5 pole in 2000, and sold as “Indusi-Messwagan” until 2011.
I hate to ruin your experience, but to be honest, it looks like they saw you coming, at least on this one. Is it possible to get a refund? This could be your best solution. Many times, sellers on eBay don’t know anything about what they are listing.
Here is the parts diagram for this model:

There is more missing than just the circuit board. While it might look encouraging, this particular model has not been produced for many years. Marklin does not list any of the parts you would need for this track cleaner. You would have to source these in the secondary market. From experience, I can tell you, to find it new will be hard maybe impossible because the circuit board may not be one shared with similar models. Your friends at eBay have them listed used from a reliable dealer in Houston Texas for about $25.00 but I am not certain he will ship to your location. I don’t know how taxes are assessed at your location, but this another concern. Other parts are also listed, but you might need to purchase other parts which includes the one you need. For example, to get that front top weight and cleaning wheel, would require you to purchase the entire frame again from this seller, or nearly the equivalent of what you already have.
Your motor looks pretty rough, and might not work. These are also nearly impossible to find. On this model, the coals extend down from the circuit board, so it might be hard to test it. This same seller just had the original 3 pole motor you would need, but they were quickly snapped up. You could contact him to see which parts he might sell. Motors go for about $30-35.00. Just search EBay for Marklin 8802.
You would also need someone to assemble this for you unless you think you could do this yourself. You might find sourcing the parts and assembling this model to be a long process which may be very costly, perhaps more than the value of this item.
If it cannot be returned I would clean it up a bit and just use this as a static yard item, perhaps what the previous owner envisioned.
Perhaps you can find another in better condition. It is an interesting but noisy little cleaner, which may draw a lot of attention on your track.
Again welcome and best wishes for your new shared hobby.
Take good care.
Dwight