Outer Limits 4x4 Board

hi, not too sure of detailss its a mates 90+ mod 2.8 lux he said he was driving down the road clicked 4th and then it locked up and rolled to a stop, had troubble getting out of 4th, got the selector into neutral finally but 4th is still sellected. starts with clutch in but clutch out its in 4th.

i think its a r series box i only know the g52's.. is it common that the r series drop gear or drop the selctor pin.

this happened on road not under any load. on 32in tires

any advice would be great cheers