I installed a LUK clutch kit, Timken TOB and a new master/slave in my '98 XJ w/ AX-15. The synchro's were on the way out in 1st gear; it wouldn't fully engage and periodically 1st gear would just pop out of gear when starting from a stop. I tried Redline in the transmission for a year or so, but didn't help. The only thing that helped to smooth the shifting other than double clutching was to add Penzoil Synchromesh gear lube.
As others have posted.... the AX-15 is known to have shifting problems as the mileage accumulates.
As others have posted.... the AX-15 is known to have shifting problems as the mileage accumulates.