So Sunday I had a CEL come on! Car was driving normal I figured a loose hose or something, when I got home I checked the hoses and couldn't find anything. So yesterday I hear a whining/hissing sound coming from the engine compartment, it seems to be coming from the oil cap so I have a few questions.

1. Can I just replace the oil cap and all is good or do you think it is the valve cover itself?

2. Where can I buy a valve cover? Big have seen post on here that say it cost about $300 but nothing on where to order one.

3. How much damage could be caused by waiting to fix this? I do not have $300 to replace this right now.

http://www.youtube.com/watch?v=Araja...ature=youtu.be
Here is a video of the noise (not my video/car)

 

You probably don't need a whole cover. You can probably just get a gasket which is pretty cheap. I can't watch the video at work so I will have to wait till I get home.

 

Modern engines have negative pressure in the crankcase for less drag on rotating / reciprocating parts, and to help with foaming. The risks, in my opinion, depend on whether the vacuum is generated by a vacuum pump, or manifold vacuum. I don't know anything about the Peugeot engines, but if the car is an "S", it has to have a pump (usually driven off the end of a camshaft), since forced induction engines have pressurized intake manifolds.

In the case of a crankcase that is pump scavenged, I don't think there is risk other than any dirt present in this area could be sucked into the valve cover, which is NOT what you want.
In the case of a crankcase that is scavenged by manifold vacuum, however, I'd be concerned about the engine running lean at idle, in addition to contaminating the oil via dirt being sucked in. If the leak was that bad, however, you would probably notice a rough idle.

Don't take my words as anything more than an uneducated guess. I really do not know about the 2nd generation cars.