Yes, you can have a leak there -- it won't be a boost leak unless you have bad PCV valves, but it could intake air (vacuum leak) and cause a faulty idle. I have a leak on the drivers side exhaust valve cover myself. Seems to cause a little erratic idle at start up, and a tiny oil leak, also. It's a lot of work to fix a simple issue, so I haven't done it yet -- waiting for something bigger :)