hmmm...some myths and legends here
the XU1 4 speed was always ..M20 on the build sheets
and came standard with different ratios to the V8 M21 box
but dont forget there were 2 others boxes homologated for use
with the XU1..the normal 6 cyl M20 used in the GTR and the
box with the same ratios as used on the L34...with a 2.32 gear set
XU1 boxes may have 1 groove 2 grooves or...NO grooves in my experience
the real check as the number of grooves can be misleading is the cluster gear part number
M20 normal ends with 496 M20 (XUI) is 899
M21 V8 cluster is 497. M21 optional L34 and XU1 is 484
as mentioned ..the cluster gear internal bearing surface is prone to wear..but
this is not the real issue. That is one example of what happens when the case
hardening gets worn through. The Cluster gear is one example...it also happens
to other case hardened parts. Part of the reason the cluster comes up first
with this fault...is that the internal oiling for the needle rollers in the cluster
is crap... One small oiling hole means little gets in...and then some idiots
put in ATF to fix up (they reckon) cold shift issues and it wont protect
the cluster (or any internals from wear) The suggestion of molybond
is an oldtimers fix for cold shift issues...
but a properly built / rebuilt aussie box has to have minimal clearances(or end floats)
and that means GOOD bearings (no chinese crap) and time...time to fix endfloat
and clearances. (Motor cycle valve shims are nice behind the bronze bushes)
and properly built, it will happily run a 140w gear oil and have no shift issues.
I build and run this sort of box in my race car and (with an annual tear down and check)
I have had 4 seasons out of the latest