On my 1994 Mercedes E320 wagon, I replaced the valve cover gasket with a new one. When I put in the 12 bolts on the valve cover and goes on top of the head, all but two of the bolts went through ok and tightened. The other two bolts did not tightened and upon looking at the threads of those two bolts, it appears to be some form of liquid on the bolts threads. The 2 bolt threads themselves are fine, no thread stripping on the bolts. It seems that the 2 inside threads on the top head are stripped and the bolts will not tightened. Here is the location of the two holes on the valve cover that the 2 bolts will not tighten on the head. (blue circle):

Is there some kind of thread repair that can be apply to the two holes on the head and be able to tighten the bolts? I believe there is something like liquid thread that can be apply on the bolts. I appreciate some comments/feedback on this issue. Thanks for reading.

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