[Axzon]

From 1987 - 1997 the 125 exc used the 502 cases.
From 1998 - 2001 the 125 exc used the 503 cases
In 2002 the 125 exc used the 523 cases

In 2000 the 125sxs used the 523 cases
In 2001 the 125sxs used the 503 cases
In 2002 the 125sxs used the 523 cases
From 2003 to 2008 the 125sxs used the 515 cases

The 512 was used in 2000 and 2001 as 125sx cases
The 515 cases were used in 2001 and from 2003 to 2012 in 125sx .
The 523 cases were used in 2002 only for the 125sx

2007 and 2008 the 515 cases were used in the 144sx engine
The 515 cases were used in the 150sx and 150xc from 2009 - 2012

That is what has been recorded for those years. Then you had the 150 engines replace the 144 ones (but only the #144 changed to 150 as the motor cc stayed at 144cc).

The difference between the engines were that the SX only had power for the ignition and CDI where the XC ones had power for lights also. As we have only been riding SX I have no knowledge about what was different (if anything) mechanically between XC and SX apart from gearbox. I do not think there was any difference in the crank and/or piston. (Thou the XC used a 2 ring piston and the SX a single ring piston) The CDI would have had a different programme better suited for XC riding.

All models were not available in all countries. But in 2008 the only small 2 stroke XC was the 144XC in USA. As you are from Spain there is a big chance that KTM in Spain (and Europe) had a 125 XC bike available.

And yes, the cases are sold as a pair as they are precision machined to give the exact tolerances for crank and gearbox when tightened up with a gasket between the two sides.

The 2008 515 engine cases are still available.