Gearbox problems, help.

[Hare]

Hi

I just came back from a trip and had to drive the last 50km on fourth gear! The fifth gear just doesn't work. There's a small hizzing sound (a bit like the one you can here when you're reversing, hizzzzzzzz) coming from the gears. This sound originally came only when I had the fifth gear on.

The fifth gear drops to neutral after few 100meters. Anyone have any idea what could be wrong. Is it the gearbox, could it be worn guides on the stick itself, what? (btw. English isn't my native language so sorry about possible typos).

The hizzing noise increases and decreases depending on the RPMs. The noise now comes with fourth gear also.

I have a bad feeling this is going to cost me a lot. Please post any information. Thanks !

My car is Renault Laguna ´94, 250 000km