Maybe they've improved their quality? Mine both leaked at the side fitting.

 

I may be wrong about 1" x 5/8."
Also I see lots of cheaper tees on eBay that are all one piece.

 

I ordered 3/4 x 3/4 and 1 x 5/8 but I see how these could leak. Bit of a bummer considering the cost.

 

I'm not a QC weld inspector, but work with some who are.
How does the outside look? A proper weld bead can be trusted with... a lot.
Is it even welded?

 

They're with the car but didn't look to be welded on the outside or inside. Definitely no bead.

 

At least I see you ordered them before I chimed in. I wasn't following the thread and actually had to search my emails for the place I bought them from for my recommendation.
Maybe contact the seller and ask him for some peace of mind (?).
Maybe they are threaded and he used some Loctite red or something.
FWIW mine are doing ok.
I think.

 

Mine were not welded. They appear to be a dry press fit.