Need help with shock absorber
 

I have noticed a bit of oil just a smuge on right rear shock absorber.
I bought new one for my FRS at Toyota with self lock nut
I brought it to 3rd party mechanic shop to install.

I figured it should be simple job.
They installed it and it was fine for two days.
On third day I heard sound coming from it and after checking all shock absorber was covered in oil and had a puddle on a ground.

Obviously somehow they screw it up. I will go back to them tomorrow, but what they could have done wrong?
Is there any trick to lock nut?
Also Toyota did not have lock nut so I bought it from Subaru for BRZ. It looked the same

I have FRS 2016 does it has the same shock absorber as BRZ 2016? If Toyota does not have this part can I use BRZ one?
Thanks.

I have heard stories of mechanics using a rattle gun on the top nut to do it up and it damaging the piston seals by over spinning the shaft but I think that is exceeding rare.

The subaru unit should be a direct equivalent.