Gadget

Got an engine back from being built, added all fluids and the diff started leaking from one bolt, I removed the pan, cleaned it all up, re sealed it putting the sealer all round the holes for the bolts, I even put some sealer on the threads of the bolts.
Re fitted and added a litre of fluid the next day. It started leaking from the same bolt almost straight away. It's not coming from the sealed joint above the bolt, it's coming from where the washer touches the housing.
Anyone else heard of or had the same problem??