If you screw a tapered adapter into it it will seal - at least the 1/4" NPT adapter for the sender for my pressure gauge does.
If you are thinking of a permanent pressure gauge VDO have a compact sender which fits in the available space with connections for both a warning light and the gauge and a 15 psi setting which might tell you a little more than the nominal 5 + - 2 psi OEM sender.
One of the German suppliers also has reproduction pods with the choice of fixing screw locations, offset like OEM or central like most aftermarket pressure gauges.
It might be easier to find a sender with the 1/4 pipe thread and use a 12mm adapter, as the range of 12 mm thread senders might not cover what you need.