回复：回复：有两个问题。。。。。

No engine oil should go through the intake manifold.  Therefore, intake manifold gasket 老化的话不会造成漏机油。Fuel injector 上老化的像皮圈不应造成漏机油。If you only saw intake manifold下面是机油, I guess it came from a leaking head gasket assuming your new valve cover seal replacement excluded the possibility of a leak from there.