Index of the gas block to barrel gas port looks good via the burn mark around the barrel gas port.
On the inside of the gas block, check the ridge around the gas block passage channel for a high ridge cause when the passage was drilled that is not allowing the entire top of channel in the gas block to mate correctly with the entire top of barrel. If needed flush the ridge with the ID of the gas block channel.
Also, when the gas block is installed on the barrel, the set screws that secure the block to the barrel have to be loctite in place. red 272 is the correct loctite, and if the allen screws need to be removed later, the insert a old allen wrench in the allen socket heads, Glow the wrench with a torch to heat the screws up to break down the loctite bond, then switch over to a new allen wrench to remove the set screws.
As for checking for leaks, CLP sprayed around the gas tube to block front and back, gas block to barrel front and back, and then use a piece of tubing on the end of the gas tube in the receiver to pressurize the gas tube to 100lb of air. Also, check the carrier key for leaks as well, hence CLP around the base of it where it sits on top of the carrier, then hold the bolt inward while pressurizing the front of the key. You should not have any leaks from the gas tube to key, block to barrel, nor key to top of carrier.
But back up, and bring me up to speed on the reason for the adjustable gas block in the first place.