Not sure that sanding the edge flat was a sensible thing to do. LR design the parts deliberately. In this case, if you look at the first photo where you have cleaned it up it shows a consistent contact point around the inner edge. The rest of the edge where the bolt holes are positioned are slightly curved down; this is probably deliberate. Think about it fitted. It has the gasket in between and as its all tightened up the bolts have a clamping effect to achieve a consistent pressure seal for the gasket. By flattening it you are reducing the clamping ability of the bolts to achieve a seal. I'd check this point with a supplier to see if new/ replacement sumps are the same.

It did cross my mind when contemplating throwing it in the bin but if you look at the original gasket, tis obvious that this 5mm area was the only bit making the seal. I could also see several spots where this area had been breached but the rest of the gasket just allowed the oil through.. Im sure a mild steel flange will react differently to a machined casting under pressure but surely it has to be void of weld pits and the like to stand a chance.

Im firing it up today so Ill report back how its looking. ;)
 

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