once installed, the layshaft does not spin. It should have zero wear at the areas touching the case, the wear will be where the bearings contacted. 

If a new layshaft spun freely during install, the case is bad.  If lightly oiled and it can be rotated in the case, not freely but not sticking, requiring a tool in the slotted end to turn it, case is good.  A brand new shaft could need a little polish.

Apply layout ink e.g. Dykem Blue to the inside of the layshaft holes in the case, if you dont have any then just use a dark color magic marker, and apply to the last inch or so of each end of the layshaft   Hold the layshaft already rotated to (about) where it needs to be when in final position, push it in until it meets resistance.  Tap it gently with a wood mallet or block.  Tap it back out and inspect the bores and the layshaft, see if there are witness marks showing a high spot in the bores.  The wear ridge that you could feel on the old shaft may have scratched the gbox bore when you removed it, if so that can be polished out.  

Check in youtube for classicminidiy. he has rebuilt a couple of trans I think. You can also check with Cole at https://www.classicminidiy.com/

Hello;  My first time rebulding an 1128 gearbox, lots of information out there including videos from our host which leads me to doing a dry build to check layshaft thrust washer clearance.  Purchased a new layshaft and bearings.  The old layshaft had wear at the larger end and there was a ridge felt by fingernail.  Turns out both the old and new layshaft would bind when about 3/4 installed, and it will turn with some resistance when fully installed.   In Tony's video he says "make sure the layshaft turns freely".  The laygear rotates well on the shaft.  Not sure if the case needs line bored at the layshaft mounting points.   A common problem?  Thanks in advance!   Andrew