Brand spanking new ThermoDynamics TDX90+ condensing boiler (it hasn't condensed anything yet) with Carlin EZPro burner and direct vent. Positive draft through the entire system (except for the 4" combustion air inlet ductwork that is), so it should leak anyplace there's any gap or hole. The positive pressures are not excessive; 0.08" water column over fire (0.12" spec) and 0.03" just past the boiler in the direct vent gas testing fitting (0.02" spec). This being a direct vent system, the pressures are not adjustable independently of air/fuel ratio. That is, there's no barometric damper (or damper of any sort) in the flue. Slight oil smell in the basement; slightly oil-smelling air is coming out near the transformer hinges, where there's no gasket. I don't know what the gasket's supposed to do anyway; there's a U-shaped cutout for the Cad cell that seems to allow any pressure to bypass under the gasket anyway, back towards the transformer hinges. I couldn't find any air coming out any of the flue piping joints, and there's zero smoke and no CO. I'll check excess air via O2 analyzer shortly.
Should I just goop the transformer lid down with silicone all the way around? Seems like that's an amateurish solution.