I recently have had a problem with oil in the plug wells on my V6.
As already said if you continue to use it you will have to live with the awful smell of burning oil when driving and sat in traffic, not to mention the risk of possible fire.
Pound to a penny if you have got oil in the wells it will be leaking out elsewhere, if not now it wont be long. This means running down the side of the engine, onto manifolds, alternator, starter and other components.
If the oil is leaking, the cause could be blocked breather pipes which can cause other problems like stalling and bad starts etc which will get worse.
My advice is to get the rocker covers changed.
I did these myself following a failed and costly attempt after sending my car to a local non Vauxhall garage due to having time constraints. A simple job they said after diagnosing it. The trouble was they let the junior mechanic have a go and from what I assessed instead of taking the plastic cover off the wiring loom to allow room to remove the n/s rocker cover he forced it off through the obstructions. This resulted in cracking the cover and breaking the gasket lips. What he did then was refit the cracked cover after trying to fill the crack wilth sealant and then force it back into place.
I had the car back and needless to say the cover still leaked. I ended up deciding to do the job myself, properly, thats when i found the cracked cover which set me back £80 plus new gaskets. When doing the one bank I did the other rocker gasket while the plenum etc was off as that would no doubt go too at some point and guess what there was oil in the wells too.
My advice again, get it done before things get worse, you may as well do both rocker gaskets, and if you can do it yourself, it takes a bit of time and messing but at least it gets done right at a great saving, if not use a trusted garage.