NP203 part-time conversion with Mile Marker output shaft

[Minnesota]

Ok, my Jedi masters. I have a problem:

1. I buy a np203 off of CList for my K20 as a builder to hot-swap with grumbly current one. Seller was a legit Chevy guy, and case has all signs of being a good trade.
2. An ORD twin-stick is installed. Much rejoicing. Works awesome, and dead sexy. This is with old grumby t-case. Works absolutely as advertised. Still does with old grumbly back installed.
3. Take said transfer case to my guy for a courtesy go through/rebuild. He's competent.
4. He discovers that it contains what looks to be the now unobtanium aftermarket full output shaft replacement part-time conversion. Much rejoicing ensues. There are no markings on said shaft to further identify. Doug Nash? Mile Marker? Shouldn't be a big deal either way? Here comes the kicker.
5. Case will spin real nice on the bench (and in the truck) in 2WD. Buuut, once you put it in 4WD, you have to pry the output shaft back to get it back in 2WD. Some sort of combo of gear bind and the spring can't do the deal.

We are scratching heads on this one. All materials are real hard, and obviously age creates looseness as opposed to tightness.

Anybody got any thoughts/experience?