PSA: BRIO ZENTO

Seems like I'm on a one woman crusade to highlight products that don't work or shoddy customer service.
My poor baby has a REALLY sore and bruised bottom today and we think it's down to the Brio Zento car seat that he uses.
We mostly do short trips in the car seat, but today we went back to Happy Chicks to return the poorly Cream Legbar. It's a 2.5 -3hr round trip depending on traffic etc.
My 2year old complained of having a sore bum on his return and kept flinching when picked up/asked to sit down. So my husband checked his bum thinking he had a sore rectum as he's had ongoing problems with having a poo and withholding said poos.
He couldn't see anything wrong so we carried on as normal.
At bathtime I decided to look at the cheeks of his bottom as he was still complaining and flinching when you touched his bottom. He looked to have bruises on the cheeks of his bottom and his lower back. He was born with a Mongolian blue spot so I questioned whether that was it (I knew in my heart that it wasn't but wanted to believe it was).
His bottom is bruised, badly :( We inspected the car seat and it is rock hard! We've never thought to inspect it in that way. My older son used the car seat for a while when he was younger, I just hope he was never subjected to such pain.
I can't believe that this happened! I feel I have subjected my child to an abuse. I strapped him into it daily, without a thought. Thank God when his older brother was not with us I let him use his car seat (kiddy comfort pro) so less pain for him I hope.
Upon Google-ing I found this thread. Seems it is a known problem. Maybe there's more info out there. It was enough for us. The car seat will be going in the bin!