5th gear on a 172

[Blackdavid]

Hello. All of a sudden my 172 ph2 started having problems with 5th gear.
Gear engages normally, but when throttle is applied the gearstick moves back a lot ( only in 5th) and the 5th disengages with a slight crunch.
Anyone had any problems with 5th gear syncros? Or should i be looking at the gearstick?

 

[Martin_172]

usually it jumps out of 5th when the box oil is low

 

[Blackdavid]

usually it jumps out of 5th when the box oil is low

I've checked and added about a liter of oil. It seems its doing the same. I've probably fucked the 5th syncros didn't I?