It sounds like they drilled a little too close for comfort to an oil galley or it has developed a hairline crack. If still under warranty get it looked at. If not, you may have to live with the thread tape and having to redo it, as the "real" repair will be a bit costly.
Any way to get access to a bore-scope to get a better look in there? If it is a crack it will need to be addressed as it will only get worse.