What I also found to be rather interesting with the roof rack that I purchased was the part in the manual that said not to drive over 80km/h (50mph) with anything on the rack.
In looking at the rack that I got, I am not totally sure how bad the crack lines are. I took the whole of the rack connector body off the rack bar and noticed that there is a metal plate that runs down through the plastic body, so the plastic might not provide all the clamping/connecting force onto the roof rail. Now I did use some fine feeler gauges as I am an ex-engineer and happen to have those sorts of things, and on one of the connector bodies with the largest crack, when you clamp it onto the rail, the crack does open up so that I can fit my smallest feeler (0.0025") in, where if you aren't clamping it doesn't slide in. so clearly there is a defect, but the other 3 you just see the line. Now Mick's garage as since said that this just a moulding mark where the two pieces are joined. I don't know if they are talking about a mould that forms the piece, or if they thing the connector body is made up of several pieces. That is still up in the air.
I bought the aluminium Nordrive rack, but they do sell several other manufacturers that might not have any issues.
2018 Niro EX - Ocean Blue
GTA - Canada.