Edward, did you try both loosening and tightening with the impact? I have gotten quite a few jammed things apart going both ways. Got many big grinding machine parts apart like that.
Otherwise because the bolt heads look well sealed it will be difficult to get anything sucked into the threads. Perhaps drill a hole through the flange down to the bolt will give the lube some access to soak in. Then you can work the manifold on a bench.
Maybe hack sawing the heads off or getting the washer to split under the head with a chisel might get some lube to soak in.
Dave Neptune
