Z drop?

Ok, when homing, the carriage doesn't want to descent the last 2mm or so unless given a bit of a shove.
I've lubricated the rails/bolts (spray lithium grease).
I've made sure the extruder wires are long enough.

Anybody know something else before I spend 2 days poking at it?

 

is your nozzle hitting the build platform?

Also what direction is your switch facing? Have you turned it around?

 

Not hitting platform (if you let it work on its own, sometimes it will fall and hit the platform )
I changed the limit switch to the right way around.

I'm printing atop an auxiliary 3/16 boro plate held in with binder clips...
I tried using top stabiliziers, but since it started doing this, I took them off to "start from 0."
About to use acetone/wd-40 on the z rails to clean them and reapply grease...

 

Good idea trying o clean it. Putting some grease/lube on the threaded rods should fix that issue

 

Did you try adjusting your z endstop bolt?