Hi. I have a 1994 Nissan Sentra 140 (South African) with a manual 5 speed gearbox. The problem lies in that I cannot use the fifth gear. It does not stay there, unless I hold it there. It started off about
1.5 years ago when it would occasionally slip out of 5th when the engine was revving high. It became progressively worse, and now I cannot use the gear at all.Any suggestions?