My left front door on a 93 Legacy is really struggling to open from the inside, I'm suspecting it's in the actual latch mechanism. Do 95-99 Legacy latches work, or am I stuck looking for a 1st gen donor car?

They are unfortunately quite rare here in MI....

First gen only, NLA from Subaru, and yes they all do that. There is a spring in the latch that wears it's retaining hole and so hasn't got the correct tension to keep the lock mechanism from interfering with the latch operation. 

 

GD

I've fixed these by adding a small spring between the mechanism (in the curved part at the bottom of the opening) and the latch "frame" to assist the older, failed spring.

 

Takes a very small spring from the hardware store.  

 

Probably won't work forever, but seems to do the trick.....the ones I've fixed have lasted years now.

I've also carefully drilled a hole next to the old spring and added a tiny screw to adjust the pre-load on it. But this takes some precision to accomplish. 

 

GD