Today when I tried entering a roundabout, my 2003 Astra's gearbox got stuck in neutral as I tried shifting to first. I finally managed to shift after wiggling the stick around and applying more force, only to get stuck in neutral again, so I decide to pull up.
After some experimenting I found out that this will only happen when the engine is running. If I try to shift to reverse, I would hear a grinding sound (this only happens when shifting to reverse, all other gears are "blocked"). If I start the engine while in first, the engine would stutter and turn off after a few seconds.
This would happen seemingly at random, sometimes I'm able to shift normally and others it would just get stuck.
It's a 2003 Opel (Vauxhall) 1.6l Astra with 200k km (130k miles). I did a yearly (mandatory) checkup a few weeks ago.
What could be the culprit here? Would a simple gearbox oil change solve it?