Astra H VXR maintenance

[Mark8815]

What’s a rough but fairly accurate price for getting the gearbox sorted? I’d rather prevent it going rather than having to fix it.
Also, I’ve read that the stem seals are a bit iffy too, so what would I be looking at to get that done?
Haven’t bought one yet but I’ve seen these issues mentioned many times. I’ve emailed my local specialist but heard nothing back yet.
Thanks