[ImperialCrown]

The inner CV axle journal that rides on the inside surface of the seal may be rough, nicked or grooved. This can rapidly wear out a replacement seal. It should be a smooth surface finish for the seal.
Give it a visual inspection for grooving and if your fingernail catches on it, the groove is to deep. A reman right axle may be the answer.

 

[Honolulu-Hack]

The inner boot was malforming and leaking grease so I changed it at the same time as the new extension housing. Both parts brand new.

What about the tranny gears that fit into the race bearings on the other end of the extension housing, where it fits to the tranny? If something is worn and not spinning on a good tight line, then that could wear on the race, malforming the race and causing loose fitting, and then more fluid running into the extension then out the seal with more pressure than it can handle?

 

[ImperialCrown]

You will have some play in an unloaded axle where it enters the transaxle. It's normal. If the differential sidegears and/or shaft splines have excessively worn, it may cause a seal leak. The seal should be able to conform to some shaft play. Are these OEM parts? I have fitted a seal onto the axle joint before installation just to test and make sure that it was a firm fit.
You might want an experienced mechanic's opinion on this leak. At 240K miles(?), this may be a differential tapered roller bearing wear issue.