This one is new to me, as I'm not an expert in repairing gearboxes. Perhaps somebody knows better the inside of it and can guide me.

 

So, the gearshift lever developed (in time) an excessive play. Now I have to "search" for the right gear. My first thought was the shift mechanism got faulty. I raised the front of the car and inspected it. To my surprise there was nothing wrong with it. Zero play . The shift rod that enters into the gearbox follows with precision the movement of the gearshift lever.  Yet the gearshift lever moves from left to right like a limp ####. 

 

Then I noticed a slight clunking noise inside the gearbox when moving the gearshift lever from left to right. One more important thing: the gearshift lever does not have a neutral position anymore. I mean it doesn't return to it.

 

I looked in the workshop manual, chapter Clutch & Manual Gearbox. My impression is that the roll pins 23 and 24 lost their stiffness or almost fell off (see photo).

 

Detail

 

A few photos made by a Polish mechanic in his workshop.

 

 

Update:

Actually the faulty part proved to be part #17. 

 

Inside that barrel there is a spring that is responsible for bringing the gearshift lever back to neutral and to assist the gears shifting. The spring broke. I found out from a Czech mechanic that the fault is quite common. Corrosion from condensation, old oil, poor spring steel, fatigue, and wear are the main causes. Note that the part can't be repaired because it is press fitted 

 

Conclusion

We have to discern between play in the shift mechanism (when the gearshift lever still springs back to neutral point) and play from inside the gearbox (when the gearshift lever remains in whatever position when in neutral).

 

I had my Czech friend send me a good second-hand part to replace the faulty one.

This is a close-up photo of the faulty part in my gearbox. As you can see there is corrosion on steel parts, most probably from previous owner who didn't change the gearbox oil every 2 years.