Seeking gearbox expert advise, lost 5th & 6th gears

[Gilles]

Yesterday after shifting into 5th, the gear did not engage... you can feel the lever "falling into the gate" but the when you release the clutch it acts like is in neutral (reminds you of a half shaft failure), and if you shift into 6th you get the same results but with a faint gear grinding.

Got the car on the ramps to ensure that both of the cables at the gearbox end were fully into their brackets and saw that the heavy duty nylon ties that I used as an extra protection (to keep the shift cables secured) are still in position.

Then proceeded to remove the console and everything on the gear lever side seems to be fine (cables wise).

Questions:

1) Is there a possibility that the end of the cable where you have the nylon round thingi (that clicks into the gearbox) has somehow worn out? Even if reverse and 1-4 gears are operating properly?

2) Or (a more sinister possibility) could be that the selector fork inside the gearbox worked itself loose and is no longer able to slide the gear on it's shaft? Are 5th and 6th gears on the same shaft?

A few years ago I saw a picture posted by Erick533 (Hergesheimer Motorsports), showing a gearbox (still installed on the car) with the rear gearbox housing removed, if the possibility of # 2 above is the cause, perhaps I may be able to secure the fork into the shaft without removing the gearbox.

Some background: This gearbox was sent to GBox in 2014 to replace the pinion and mainshaft bearings that had failed and they also replaced the 3rd and 2nd gear synchros (along with a OS Giken LSD).

The gearbox worked very smooth and never had an issue until now (20k miles later)..

Any comments will be greatly appreciated, as I had to drive the car today on 4th gear because my other car, an Alfa Romeo, is also down for repairs (when it rains..)

Thank you in advance for your suggestions