I have a Class C200 CDI Mercedes Avantgarde Model W204 Manufacture Year 2009.
During the Technical control, I was surprised that the back right wheel service brake is not functioning, and the hand brake is also not functioning on this same wheel.
The technical report mentioned an imbalance of more than 90% for both brakes.
However I have nothing mentioned as messages on the main board of the car.
I took my car to the Mercedes approved shop, they machined the hand brake cylinders and it improved the hand brake balance (the inbalance has reduced to 35% now)
but the service brake is still not being fixed, after deep investigation they advised me that the ABS bloc (part number A 204 431 37 12 ) is damaged (when pumping with the brake, the hydraulic oil is not coming out from the outlet going to the HR liner going to the back right wheel) and they mentuioned to me that this latter need to be replaced, but the spare part is not available and need to be ordered on demand.
I decided to consult an other garage whom provided me with a used spare part with different part number A 204 431 53 12 since the A 204 431 37 12 is not available.

My questions:
1- Is it normal that the onboard computer do not any ABS mulfunctuion message dur to this issue ?
2- Is it normal that the service brake and the hand brake are mulfunctionning on the same back right wheel only? could it be another cause for this problem rather than the ABS block?
3- What could be the cause of this issue ?
4- Is it Ok to replace the ABS bloc part number A 204 431 37 12 with the part number A 204 431 53 12 ?
5- What are the differences between the ABS bloc part number A 204 431 37 12 with the part number A 204 431 53 12 ?

Knowing that I proceeded to the replacement of the part number A 204 431 37 12 with the part number A 204 431 53 12 and since that the brake seem working fine except that when I press hard on the brake, I'm hearing a spongy air sound !!! which I'm not sure if it was there before or not , or it is just caused by the new replacement.???