ABS replacement 2007 Mazda2…Thoughts?

Hello and nice to meet you.
I own a 2007 Mazda 2 and I bought it second hand.
I am having a problem with the ABS (there is no ABS light blinking).
So there is a chance that braking may stop working. It may happen once per month or twice per day.
I press the brake and it halts(i can't press it anymore-it becomes very hard). I had to release it
and then press it in order to work(although once i had to release it twice in order to finally work).
Under such a condition it looks like ice skating.
A verified engineer told me that it's a well known issue(1 out of 10 had this).
He told me that i have to change the ABS pump and ABS control unit.
There is a 'cheap' solution and an expensive one.
The latter is to buy a new one and the former to buy a used one.
So my question is , do you have to propose a place to buy a used one in Europe?
As far as i can understand there is no way to test the used one for any defects.
I mean it may break after 6 months and nobody can predict that.
What do you propose ?
Thank you very much.
 
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