318 LA rear main leak?

Ok so I pulled the sump tonight & removed the rear main cap all looked ok
I removed the lower seal & fitted the main cap with tight bolts & same gap was apparent.
then I removed the top seal & rear cap bearing shell & refitted & same thing I have a gap.
then I checked the rear cap with a straight edge after removing again to find that it looks flat to me & it should sit flush on the block.
Here are some pics