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Did you solder it to the 90* elbow or consider brazing the ends to the block to seal it up 100%?
I did solder the elbow to the tube but I would recommend not trying to braze the tube to the block.
Brazing requires a lot of heat.
Clean the valley hole really well with brake cleaner and smear some rtv sealant on the outside of the elbow on the final fit/assembly.